The Collaborative International Dictionary of English v.0.48:

Authority \Au*thor"i*ty\, n.; pl. Authorities. [OE. autorite,
   auctorite, F. autorit['e], fr. L. auctoritas, fr. auctor. See
   Author, n.]
   1. Legal or rightful power; a right to command or to act;
      power exercised buy a person in virtue of his office or
      trust; dominion; jurisdiction; authorization; as, the
      authority of a prince over subjects, and of parents over
      children; the authority of a court.
      [1913 Webster]

            Thus can the demigod, Authority,
            Make us pay down for our offense.     --Shak.
      [1913 Webster]

            By what authority doest thou these things ? --Matt.
                                                  xxi. 23.
      [1913 Webster]

   2. Government; the persons or the body exercising power or
      command; as, the local authorities of the States; the
      military authorities. [Chiefly in the plural.]
      [1913 Webster]

   3. The power derived from opinion, respect, or esteem;
      influence of character, office, or station, or mental or
      moral superiority, and the like; claim to be believed or
      obeyed; as, an historian of no authority; a magistrate of
      great authority.
      [1913 Webster]

   4. That which, or one who, is claimed or appealed to in
      support of opinions, actions, measures, etc. Hence:
      (a) Testimony; witness. "And on that high authority had
          believed." --Milton.
      (b) A precedent; a decision of a court, an official
          declaration, or an opinion, saying, or statement
          worthy to be taken as a precedent.
      (c) A book containing such a statement or opinion, or the
          author of the book.
      (d) Justification; warrant.
          [1913 Webster]

                Wilt thou be glass wherein it shall discern
                Authority for sin, warrant for blame. --Shak.
          [1913 Webster]

WordNet (r) 3.0 (2006):

authority
    n 1: the power or right to give orders or make decisions; "he
         has the authority to issue warrants"; "deputies are given
         authorization to make arrests"; "a place of potency in the
         state" [syn: authority, authorization, authorisation,
         potency, dominance, say-so]
    2: (usually plural) persons who exercise (administrative)
       control over others; "the authorities have issued a curfew"
    3: an expert whose views are taken as definitive; "he is an
       authority on corporate law"
    4: freedom from doubt; belief in yourself and your abilities;
       "his assurance in his superiority did not make him popular";
       "after that failure he lost his confidence"; "she spoke with
       authority" [syn: assurance, self-assurance, confidence,
       self-confidence, authority, sureness]
    5: an administrative unit of government; "the Central
       Intelligence Agency"; "the Census Bureau"; "Office of
       Management and Budget"; "Tennessee Valley Authority" [syn:
       agency, federal agency, government agency, bureau,
       office, authority]
    6: official permission or approval; "authority for the program
       was renewed several times" [syn: authority,
       authorization, authorisation, sanction]
    7: an authoritative written work; "this book is the final
       authority on the life of Milton"

Moby Thesaurus II by Grady Ward, 1.0:

426 Moby Thesaurus words for "authority":
   Admirable Crichton, acme, adept, administration, adviser,
   affidavit, aficionado, agency, agentship, amateur, amperage,
   announcer, annunciator, appurtenance, arbiter,
   arbiter elegantiarum, arbiter of taste, armipotence, artisan,
   artist, artiste, ascendancy, assignment, attache, attestation,
   authoritativeness, authorities, authority, authorization,
   be-all and end-all, beef, bill of health, birthright, black power,
   blue ribbon, bon vivant, brevet, brute force, buff, care,
   certificate, certificate of proficiency, certification,
   championship, channel, charge, charisma, charm, claim, claws,
   clearance, clout, clutches, cogence, cogency, cognoscente,
   collector, command, commission, commissioning, commitment,
   communicant, communicator, compulsion, conduct, conjugal right,
   connaisseur, connoisseur, consequence, consignment, consultant,
   control, cordon bleu, countenance, crack shot, craftsman,
   credential, credit, critic, cure, dead shot, delegated authority,
   delegation, demand, deposition, deputation, devolution,
   devolvement, dilettante, dint, diploma, diplomat, diplomatist,
   direction, directorship, disposition, divine right, doctor,
   dominance, domination, dominion, drive, droit, due, duress, effect,
   effectiveness, effectuality, elder, elder statesman, embassy,
   eminence, empery, empire, empowerment, enabling, enchantment,
   energy, enfranchisement, enlightener, entitlement, entrusting,
   entrustment, epicure, epicurean, errand, establishment, esteem,
   evidence, example, executorship, exemplar, exequatur,
   experienced hand, experimental scientist, expert,
   expert consultant, expert witness, factorship, faculty, fan, favor,
   fiat, first place, first prize, flower power, force, force majeure,
   forcefulness, freak, full blast, full force, full power,
   good feeling, good judge, gossipmonger, gourmand, gourmet,
   governance, government, graduate, grapevine, great soul, greatness,
   grip, guidance, guru, hand, handling, hands, handy man, headship,
   hegemony, height, highest, hold, husbandry, ideal, illuminate,
   imperium, importance, inalienable right, incidental power,
   influence, influentiality, influentialness, informant,
   information center, information medium, informer, insinuation,
   intellect, intellectual, interest, interviewee, iron hand,
   journeyman, judge, jurisdiction, justness, kingship, lead,
   leadership, leading, legation, leverage, license, lieutenancy,
   lordship, lover of wisdom, magisterialness, magnetism, mahatma,
   main force, main strength, man of intellect, man of science,
   man of wisdom, mana, management, managery, managing, mandarin,
   mandate, manipulation, marksman, master, mastermind, mastership,
   mastery, maven, maximum, mentor, might, might and main, mightiness,
   mission, model, moment, monitor, most, mouthpiece, moxie,
   muscle power, navicert, ne plus ultra, new high, newsmonger,
   no slouch, notarized statement, note, notifier, nut, office,
   officialdom, officials, oracle, ordering, palms, paramountcy,
   past master, pattern, personality, persuasion, philosopher,
   pilotage, pizzazz, plenipotentiary power, police, politician, poop,
   potence, potency, potentiality, power, power of attorney,
   power pack, power structure, power struggle, power to act,
   powerfulness, powers that be, practical scientist, precedence,
   predominance, preponderance, prepotency, prerogative, prescription,
   presidency, press, pressure, prestige, presumptive right, pretense,
   pretension, primacy, priority, pro, procuration, productiveness,
   productivity, professional, professor, proficient, prominence,
   proper claim, property right, proxy, public relations officer,
   publisher, puissance, pull, punch, pundit, purchase, purview, push,
   rabbi, radio, raj, rank, ratification, record, refined palate,
   regency, regentship, regnancy, regulation, reign, reporter, repute,
   responsibility, right, rishi, rule, running, sage, sanction,
   sapient, savant, say, say-so, scholar, scientist, seer, seniority,
   shark, sharp, sheepskin, sinew, solidity, soundness, source,
   sovereignty, specialist, spokesman, standard, starets, statesman,
   stature, steam, steerage, steering, strength, strings, strong arm,
   suasion, substantiality, subtle influence, suggestion, superiority,
   superpower, supremacy, sway, sworn statement, talons, task,
   technical adviser, technical expert, technician, technologist,
   television, teller, testamur, testimonial, testimony, the conn,
   the helm, the wheel, thinker, ticket, tipster, title, top spot,
   tout, trust, trusteeship, upper hand, validity, vehemence,
   vested interest, vested right, vicarious authority, vigor, vim,
   virility, virtue, virtuoso, virulence, visa, vise, vitality,
   voucher, warrant, warranty, wattage, weight, weightiness,
   whip hand, wise man, wise old man, witness, wizard, word, zenith



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

AUTHORITY, contracts. The delegation of power by one person to another.
     2. We will consider, 1. The delegation 2. The nature of the authority.
3. The manner it is to be executed. 4. The effects of the authority.
     3.-1. The authority may be delegated by deed, or by parol. 1. It may
be delegated by deed for any purpose whatever, for whenever an authority by
parol would be sufficient, one by deed will be equally so. When the
authority is to do something which must be performed through the medium of a
deed, then the authority must also be by deed, and executed with all the
forms necessary, to render that instrument perfect; unless, indeed, the
principal be present, and verbally or impliedly authorizes the agent to fix
his name to the deed; 4 T. R. 313; W. Jones, R. 268; as, if a man be
authorized to convey a tract of land, the letter of attorney must be by
deed. Bac. Ab. h.t.; 7 T. R. 209; 2 Bos. & Pull, 338; 5 Binn. 613;. 14 S. &
A. 331; 6 S. & R. 90; 2 Pick. R. 345; 6 Mass. R. 11; 1 Wend. 424 9 Wend. R.
54, 68; 12 Wend. R. 525; Story, Ag. Sec. 49; 3 Kent, Com. 613, 3d edit.; 3
Chit. Com. Law, 195. But it does not require a written authority to sign an
unscaled paper, or a contract in writing not under seal. Paley on Ag. by
Lloyd, 161; Story, Ag. Sec. 50.
     4.-2. For many purposes, however, the authority may be by parol,
either in writing not under seal, or verbally, or by the mere employment of
the agent. Pal. on Agen. 2. The exigencies of commercial affairs render such
an appointment indispensable; business would be greatly embarrassed, if a
regular letter of attorney were required to sign or negotiate a promissory
note or bill of exchange, or sell or buy goods, or write a letter, or
procure a policy for another. This rule of the common law has been adopted
and followed from the civil law. Story, Ag. Sec. 47; Dig. 3, 3, 1, 1 Poth.
Pand. 3, 3, 3; Domat, liv. 1, tit. 15, Sec. 1, art. 5; see also 3 Chit. Com.
Law, 5, 195 7 T. R. 350.
     5.-2. The authority given must have been possessed by the person who
delegates it, or it will be void; and it must be of a thing lawful, or it
will not justify the person to whom it is given. Dyer, 102; Kielw. 83. It is
a maxim that delegata potestas non potest delegari, so that an agent who has
a mere authority must execute it himself, and cannot delegate his authority
to a sub-agent. See 5 Pet. 390; 3 Story, R. 411, 425; 11 Gill & John. 58;
26 Wend. 485; 15 Pick. 303, 307; 1 McMullan, 453; 4 Scamm. 127, 133; 2
Inst. 597. See Delegation.
     6. Authorities are divided into general or special. A general authority
is one which extends to all acts connected with a particular employment; a
special authority is one confined to "an individual instance." 15 East, 408;
Id. 38.
     7. They are also divided into limited and unlimited. When the agent is
bound by precise instructions, it is limited; and unlimited when be is left
to pursue his own discretion. An authority is either express or implied.
     8. An express authority may be by deed of by parol, that is in writing
not under seal, or verbally.. The authority must have been actually given.
     9. An implied authority is one which, although no proof exists of its
having been actually given, may be inferred from the conduct of the
principal; for example, when a man leaves his wife without support, the law
presumes he authorizes her to buy necessaries for her maintenance; or if a
master, usually send his servant to buy goods for him upon credit, and the
servant buy some things without the master's orders, yet the latter will be
liable upon the implied authority. Show. 95; Pal. on Ag. 137 to 146.
    10.-3. In considering in what manner the authority is to be executed,
it will be necessary to examine, 1. By whom the authority must be executed.
2. In what manner. 3. In what time.
    11.-1. A delegated authority can be executed only by the person to
whom it is given, for the confidence being personal, cannot be assigned to a
stranger. 1 Roll. Ab. 330 2 Roll. Ab. 9 9 Co. 77 b.; 9 Ves. 236, 251 3 Mer.
R. 237; 2 M. & S. 299, 301.
    12. An authority given to two cannot be executed by one. Co. Litt. 112
b, 181 b. And an authority given to three jointly and separately, is not, in
general, well executed by two. Co. Litt. 181 b; sed vide 1 Roll. Abr. 329,
1, 5; Com. Dig. Attorney, C 8 3 Pick. R. 232; 2 Pick. R. 345; 12 Mass. R.
185; 6 Pick. R. 198; 6 John. R. 39; Story, Ag. Sec. 42. These rules apply to
on authority of a private nature, which must be executed by all to whom it
is given; and not to a power of a public nature, which may be executed by
all to whom majority. 9 Watts, R. 466; 5 Bin. 484, 5; 9 S, & R. 99. 2. When
the authority is particular, it must in general be strictly pursued, or it
will be void, unless the variance be merely circumstantial. Co. Litt. 49 b,
303, b; 6 T. R. 591; 2 H. Bl. 623 Co. Lit. 181, b; 1 Tho. Co. Lit. 852.
    13.-2. As to the form to be observed in the execution of an authority,
it is a general rule that an act done under a power of attorney must be done
in the name Of the person who gives a power, and not in the attorney's name.
9 Co. 76, 77. It has been holden that the name of the attorney is not
requisite. 1 W. & S. 328, 332; Moor, pl. 1106; Str. 705; 2 East, R. 142;
Moor, 818; Paley on Ag. by Lloyd, 175; Story on Ag. Sec. 146 T 9 Ves. 236: 1
Y. & J. 387; 2 M. & S. 299; 4 Campb. R. 184; 2 Cox, R. 84; 9 Co. R. 75; 6
John. R. 94; 9 John. Pi,. 334; 10 Wend. R. 87; 4 Mass. R. 595; 2 Kent, Com.
631, 3d ed. But it matters not in what words this is done, if it
sufficiently appear to be in the name of the principal, as, for A B, (the
principal,) C D, (the attorney,) which has been held to be sufficient. See
15 Serg. & R. 55; 11 Mass. R. 97; 22 Pick. R. 168; 12 Mass. R. 237 9 Mass.
335; 16 Mass. R. 461; 1 Cowen, 513; 3 Wend. 94; Story, Ag. Sec. 154,275,
278, 395; Story on P. N., 69; 2 East, R. 142; 7 Watt's R. 121 6 John. R. 94.
But see contra, Bac. Ab. Leases, J 10; 9 Co, 77; l Hare & Wall. Sel. Dec.
426.
    14.-3. The execution must take place during the continuance, of the
authority, which is determined either by revocation, or performance of the
commission.
    15. In general, an authority is revocable, unless it be given as a
security, or it be coupled with an interest. 3 Watts & Serg. 14; 4 Campb. N.
P. 272; 7 Ver. 28; 2 Kent's Com. 506; 8 Wheat. 203; 2 Cowen, 196; 2 Esp. N.
P. Cases, 565; Bac. Abr. h.t. The revocation (q.v.) is either express or
implied; when it is express and made known to the person authorized, the
authority is at an end; the revocation is implied when the principal dies,
or, if a female, marries; or the subject of the authority is destroyed, as
if a man have authority to sell my house, and it is destroyed by fire or to
buy for me a horse, and before the execution of the authority, the horse
dies.
    16. When once the agent has exercised all the authority given to him,
the authority is at an end.
    17.-4. An authority is to be so construed as to include all necessary
or usual means of executing it with effect 2 H. Bl. 618; 1 Roll. R. 390;
Palm. 394 10 Ves. 441; 6 Serg. & R. 149; Com'. Dig. Attorney, C 15; 4 Campb.
R. 163 Story on Ag. 58 to 142; 1 J. J. Marsh. R. 293 5 Johns. R. 58 1 Liv.
on Ag. 103, 4 and when the agent acts, avowedly as such, within his
authority, he is not personally responsible. Pal. on Ag. 4, 5. Vide,
generally, 3 Vin. Ab. 416; Bac. Ab. h. f.; 1 Salk. 95 Com. Dig. h.t., and
the titles there referred to. 1 Roll. Ab. 330 2 Roll. Ab. 9 Bouv. Inst.
Index, h.t. and the articles, Attorney; Agency;  Agent; Principal.



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

AUTHORITY, government. The right and power which an officer has in the
exercise of a public function to compel obedience to his lawful commands. A
judge, for example, has authority to enforce obedience to his not being
correct. Merlin, Repertoire, mot Authentique.