The Collaborative International Dictionary of English v.0.48:

Principal \Prin"ci*pal\, n.
   1. A leader, chief, or head; one who takes the lead; one who
      acts independently, or who has controlling authority or
      influence; as, the principal of a faction, a school, a
      firm, etc.; -- distinguished from a subordinate,
      abettor, auxiliary, or assistant.
      [1913 Webster]

   2. Hence: (Law)
      (a) The chief actor in a crime, or an abettor who is
          present at it, -- as distinguished from an accessory.
      (b) A chief obligor, promisor, or debtor, -- as
          distinguished from a surety.
      (c) One who employs another to act for him, -- as
          distinguished from an agent. --Wharton. --Bouvier.
          --Burrill.
          [1913 Webster]

   3. A thing of chief or prime importance; something
      fundamental or especially conspicuous. Specifically:
      (a) (Com.) A capital sum of money, placed out at interest,
          due as a debt or used as a fund; -- so called in
          distinction from interest or profit.
      (b) (Arch. & Engin.) The construction which gives shape
          and strength to a roof, -- generally a truss of timber
          or iron, but there are roofs with stone principals.
          Also, loosely, the most important member of a piece of
          framing.
      (c) (Mus.) In English organs the chief open metallic stop,
          an octave above the open diapason. On the manual it is
          four feet long, on the pedal eight feet. In Germany
          this term corresponds to the English open diapason.
      (d) (O. Eng. Law) A heirloom; a mortuary. --Cowell.
      (e) pl. The first two long feathers of a hawk's wing.
          --Spenser. --J. H. Walsh.
      (f) One of turrets or pinnacles of waxwork and tapers with
          which the posts and center of a funeral hearse were
          formerly crowned. --Oxf. Gloss.
      (g) A principal or essential point or rule; a principle.
          [Obs.]
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Principal \Prin"ci*pal\, a. [F., from L. principalis. See
   Prince.]
   1. Highest in rank, authority, character, importance, or
      degree; most considerable or important; chief; main; as,
      the principal officers of a Government; the principal men
      of a state; the principal productions of a country; the
      principal arguments in a case.
      [1913 Webster]

            Wisdom is the principal thing.        --Prov. iv. 7.
      [1913 Webster]

   2. Of or pertaining to a prince; princely. [A Latinism]
      [Obs.] --Spenser.
      [1913 Webster]

   Principal axis. See Axis of a curve, under Axis.

   Principal axes of a quadric (Geom.), three lines in which
      the principal planes of the solid intersect two and two,
      as in an ellipsoid.

   Principal challenge. (Law) See under Challenge.

   Principal plane. See Plane of projection
      (a), under Plane.

   Principal of a quadric (Geom.), three planes each of which
      is at right angles to the other two, and bisects all
      chords of the quadric perpendicular to the plane, as in an
      ellipsoid.

   Principal point (Persp.), the projection of the point of
      sight upon the plane of projection.

   Principal ray (Persp.), the line drawn through the point of
      sight perpendicular to the perspective plane.

   Principal section (Crystallog.), a plane passing through
      the optical axis of a crystal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

principal
    adj 1: most important element; "the chief aim of living"; "the
           main doors were of solid glass"; "the principal rivers of
           America"; "the principal example"; "policemen were
           primary targets"; "the master bedroom"; "a master switch"
           [syn: chief(a), main(a), primary(a),
           principal(a), master(a)]
    n 1: the original amount of a debt on which interest is
         calculated
    2: the educator who has executive authority for a school; "she
       sent unruly pupils to see the principal" [syn: principal,
       school principal, head teacher, head]
    3: an actor who plays a principal role [syn: star,
       principal, lead]
    4: capital as contrasted with the income derived from it [syn:
       principal, corpus, principal sum]
    5: (criminal law) any person involved in a criminal offense,
       regardless of whether the person profits from such
       involvement
    6: the major party to a financial transaction at a stock
       exchange; buys and sells for his own account [syn:
       principal, dealer]

Moby Thesaurus II by Grady Ward, 1.0:

203 Moby Thesaurus words for "principal":
   A per se, English horn, academic dean, ace, administration,
   administrator, all-absorbing, arch, assets, backing, banner,
   bassoon, block flute, bombard, boss, bourdon, capital,
   capital gains distribution, capital structure, capitalization,
   cardinal, cash reserves, cello, central, chairman, champion,
   chancellor, chief, chief executive officer, circulating capital,
   claribel, clarinet, clarion, commander, concert flute, controlling,
   cornet, cornopean, corpus, cromorna, crowning, cymbel,
   danseur noble, dean, dean of men, dean of women, diapason,
   director, diva, dominant, doyen, doyenne, dulciana,
   electronics king, equity capital, feature attraction, first,
   first tragedian, fixed capital, floating capital, flute stop,
   focal, foremost, foundation stop, fourniture, front, fugleman,
   fund, gamba, gedeckt, gemshorn, genius, great, harmonic flute,
   head, headliner, headmaster, headmistress, headmost, heavy lead,
   hegemonic, hero, heroine, high priest, higher-up, highest, honcho,
   hybrid stop, important, important person, investment,
   jeune premier, key, king, kingfish, kingpin, koppel flute, larigot,
   laureate, lead, leader, leading, leading lady, leading light,
   leading man, luminary, magisterial, maiden, main, major,
   managing director, master, master spirit, melodia, mixture, money,
   moneyed capital, mutation stop, nazard, nonpareil, oboe, octave,
   organ stop, outstanding, overriding, overruling, owner, paragon,
   paramount, personage, piccolo, plein jeu, posaune, predominant,
   preeminent, premier, preponderant, president, prevailing,
   prima ballerina, prima donna, primal, primary, prime, prodigy,
   prominent, proprietor, protagonist, provost, quint, quintaten,
   rank, ranket, ranking, rector, reed stop, register, resources,
   rohr flute, ruler, ruling, senior, sesquialtera, shawm, singer,
   sovereign, spitz flute, star, starring, stellar, stop,
   stopped diapason, stopped flute, string diapason, string stop,
   supereminent, superintendent, superior, superman, superstar,
   supervisor, supreme, the greatest, the most, tierce, top dog,
   topflight, topmost, tremolo, trombone, trumpet, twelfth,
   unda maris, uppermost, venture capital, vibrato, vice-chancellor,
   viola, virtuoso, voix celeste, vox angelica, vox humana,
   working capital



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRINCIPAL. This word has several meanings. It is used in opposition to
accessary, to show the degree of crime committed by two persons; thus, we
say, the principal is more guilty than the accessary after the fact.
     2. In estates, principal is used as opposed to incident or accessory;
as in the following rule: "the incident shall pass by the grant of the
principal, but not the principal by the grant of the incident. Accessorium
non ducit, sed sequitur suum principale." Co. Litt. 152, a.
     3. It is used in opposition to agent, and in this sense it signifies
that the principal is the prime mover.
     4. It is used in opposition to interest; as, the principal being
secured tho interest will follow.
     5. It is used also in opposition to surety; thus, we say the principal
is answerable before the surety.
     6. Principal is used also to denote the more important; as, the
principal person.
     7. In the English law, the chief person in some of the inns of chancery
is called principal of the house. Principal is also used to designate the
best of many things as, the best bed, the best table, and the like.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRINCIPAL, contracts. One who, being competent to contract, and who is sui
juris, employs another to do any act for his own benefit, or on his own
account.
     2. As a general rule, it may be said, that every person, sui juris, is
capable of being a principal, for in all cases where a man has power as
owner, or in his own right to do anything, he may do it by another. 16 John.
86; 9 Co. 75; Com. Dig. Attorney, C 1; Heinec. ad Pand. P. 1, lib. 3, tit.
Sec. 424.
     3. Married women, and persons who are deprived of understanding, as
idiots, lunatics, and others, not sui juris, are wholly incapable of
entering into any contract, and, consequently, cannot appoint an agent.
Infants and married women are generally, incapable but, under special
circumstances, they may make such appointments. For instance, an infant may
make an attorney, when it is for his benefit; but lie cannot enter into any
contract which is to his prejudice. Com. Dig. Enfant, C 2; Perk. 13; 9 Co.
75; 3 Burr. 1804. A married woman cannot, in general, appoint an agent or
attorney, and when it is requisite that one should be appointed, the husband
generally appoints for both. Perhaps for her separate property she may, with
her husband, appoint an agent or attorney; Cro. Car. 165,; 2 Leon. 200; 2
Bulst. R. 13; but this seems to be doubted. Cro. Jac. 617; Yelv. 1; 1
Brownl. 134; 2 Brownl. 248; Adams' Ej. 174; Runn. Ej. 148.
     4. A principal has rights which he can enforce, and is liable to
obligations which he must perform. These will be briefly considered: 1. The
rights to which principals are entitled arise from obligations due to them
by their agents, or by third persons.
     5.-1st. The rights against their agents, are, 1. To call them to an
account at all times, in relation to the business of their agency. 2. When
the agent violates his obligations to his principal, either by exceeding his
authority, or by positive misconduct, or by mere negligence or omissions in
the discharge of the functions of his agency, or in any other manner, and
any loss or damage falls on his principal, the latter will be entitled to
full indemnity. Paley on Ag. by Lloyd, 7, 71, 74, and note 2 12 Pick. 328; 1
B. & Adolph. 415; 1 Liverm. Ag. 398. 3. The principal has a right to
supersede his agent, where each may maintain a suit against a third person,
by suing in his own name; and he may, by his own intervention, intercept,
suspend, or extinguish the right of the agent under the contract. Paley Ag.
by Lloyd, 362; 7 Taunt. 237, 243; 1 M. & S. 576 1 Liverm. Ag. 226-228; 2 W.
C. C. R. 283; 3 Chit. Com. Law, 201-203.
     6.-2d. The principal's rights against third persons. 1. When a contract
is made by the agent with a third person in the name of his principal, the
latter may enforce it by action. But to this rule there are some exceptions
1st. When the instrument is under seal, and it has been exclusively made
between the agent and the third person; as, for example, a charter party or
bottomry bond in this case the principal cannot sue on it. See 1 Paine, Cir.
R. 252; 3 W. C. C. R. 560; 1 M. &. S. 573; Abbott, Ship, pt. 3, c. 1, s. 2.
2d. When an exclusive credit is given to and by the agent, and therefore the
principal cannot be considered in any manner a party to the contract,
although he may have authorized it, and be entitled to all the benefits
arising from it. The case of a foreign factor, buying or selling goods, is
an example of this kind: he is treated as between himself and the other
party, as the sole contractor, and the real principal cannot sue or be sued
on the contract. This, it has been well observed, is a general rule of
commercial law, founded upon the known usage of trade; and it is strictly
adhered to for the safety and convenience of foreign commerce. Story, Ag.
Sec. 423; Smith Mer. Law, 66; 15 East, R. 62; 9 B. & C. 87. 3d. When the
agent, has a lien or claim upon the property bought or sold, or upon its
proceeds, when it equals or exceeds the amount of its value. Story, Ag. Sec.
407, 408, 424.
     7.-2. But contracts are not unfrequently made without mentioning the
name of the principal; in such case he may avail himself of the agreement,
for the contract will be treated as that of the principal, as well as of the
agent. Story, Ag. Sec. 109, 111, 403, 410, 417, 440; Paley, Ag. by Lloyd,
21, 22; Marsh. Ins. b. 1, c. 8, Sec. 3, p. 311; 2 Kent's Com. 3d edit. 630;
3 Chit. Com. Law, 201; vide 1 Paine's C. C. Rep. 252.
     8.-3. Third persons are also liable to the principal for any tort or
injury done to his property or rights in the course of the agency. Pal. Ag.
by Lloyd, 363; Story, Ag. Sec. 436; 3 Chit. Com. Law, 205, 206; 15 East, R.
38.
     9.-2. The liabilities of the principal are either to his agent or to
third persons.
    10.-1st. The liabilities of the principal to his agent, are, 1. To
reimburse him all expenses he may have lawfully incurred about the agency.
Story, Ag. Sec. 335 Story, Bailm. Sec. 196, 197; 2 Liv. Ag. 11 to 33.
     2. To pay him his commissions as agreed upon, or according to the usage
of trade, except in cases of gratuitous agency. Story, Ag. Sec. 323; Story,
Bailm. 153, 154, 196 to 201. 3. To indemnify the agent when he has sustained
damages in consequence of the principal's conduct for example, when the
agent has innocently sold the goods of a third person, under the direction
or authority of his principal, and a third person recovers damages against
the agent, the latter will be entitled to reimbursement from the principal.
Pal. Ag. by Lloyd, 152, 301; 2 John. Cas. 54; 17 John. 142; 14 Pick. 174.
    11.-2d. The liabilities of the principal to third persons, are, 1. To
fulfill all the engagements made by the agent, for or in the name of the
principal, and which come within the scope of his authority. Story, Ag. Sec.
126.
     2. When a man stands by and permits another to do an act in his name,
his authority will be presumed. Vide Authority, and 2 Kent, Com. 3d edit.
614; Story, Ag. Sec. 89, 90, 91; and articles Assent; Consent.
     3. The principal is liable to third persons for the misfeasance,
negligence, or omission of duty of his agent; but he has a remedy over
against the agent, when the injury has occurred in consequence of his
misconduct or culpable neglect; Story, Ag. Sec. 308; Paley, Ag. by Lloyd,
152, 3; 1 Metc. 560; 1 B. Mont. 292; 5 B. Monr. 25; 9 W. & S. 72; 8 Pick.
23; 6 Gill & John. 292; 4 Q. B. 298; 1 Hare & Wall. Sel. Dee. 467; Dudl. So.
Car. R. 265, 268; 5 Humph. 397; 2 Murph. 389; 1 Ired. 240; but the principal
is not liable for torts committed by the agent without authority. 5 Humph.
397; 2 Murph. 389; 19 Wend. 343; 2  Metc. 853. A principal is also liable
for the misconduct of a sub-agent, when retained by his direction, either
express or implied. 1 B. & P. 404; 15 East, 66.
    12. The general, rule, that a principal cannot be charged with injuries
committed by his agent without his assent, admits of one exception, for
reasons of policy. A sheriff is liable, even under a penal statute, for all
injurious acts, willful or negligent, done by his appointed officers, colore
officii, when charged and deputed by him to execute the law. The sheriff is,
therefore, liable where his deputy wrongfully executes a writ; Dougl. 40; or
where he takes illegal fees. 2 E. N. P. C. 585.
    13. But the principal may be liable for his agent's misconduct, when he
has agreed, either expressly or by implication, to be so liable. 8 T. R.
531; 2 Cas. N. P. C. 42. Vide Bouv. Inst. Index, h.t.; Agency; Agent.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRINCIPAL, crim. law. A principal is one who is the actor in the commission
of a crime.
     2. Principals are of two kinds; namely, 1. Principals in the first
degree, are those who have actually with their own hands committed the fact,
or have committed it through an innocent agent incapable himself, of doing
so; as an example of the latter kind, may be mentioned the case of a person
who incites a child wanting discretion, or a person non compos, to the
commission of murder, or any other crime, the incitor, though absent, when
the crime was committed, is, ex necessitate, liable for the acts of his
agent and is a principal in the first degree. Fost. 340; 1 East, P. C. 118;
1 Hawk. c. 31, s. 7; 1 N. R. 92; 2 Leach, 978. It is not requisite that each
of the principals should be present at the entire transaction. 2 East, P. C.
767. For example, where several persons agree to forge an instrument, and
each performs some part of the forgery in pursuance of the common plan, each
is principal in the forgery, although one may be away when it is signed. R.
& R. C. C. 304; Mo. C. C. 304, 307.
     3.-2. Principals in the second degree, are those who were present
aiding and abetting the commission of the fact. They are generally termed
aiders and abettors, and sometimes, improperly, accomplices. (q.v.) The
presence which is required in order to make a man principal in the second
degree, need not be a strict actual, immediate presence, such a presence as
would make him an eye or ear witness of what passes, but may be a
constructive presence. It must be such as may be sufficient to afford aid
and assistance to the principal in the first degree. 9 Pick. R. 496; 1
Russell, 21; Foster, 350.
     4. It is evident from the definition that to make a wan a principal, he
must be an actor in the commission of the crime and, therefore, if a man
happen merely to be present when a felony is committed without taking any
part in it or aiding those who do, he will not, for that reason, be
considered a principal. 1 Hale, P. C. 439; Foster, 350.