The Collaborative International Dictionary of English v.0.48:

Proper \Prop"er\, a. [OE. propre, F. propre, fr. L. proprius.
   Cf. Appropriate.]
   [1913 Webster]
   1. Belonging to one; one's own; individual. "His proper good"
      [i. e., his own possessions]. --Chaucer. "My proper son."
      --Shak.
      [1913 Webster]

            Now learn the difference, at your proper cost,
            Betwixt true valor and an empty boast. --Dryden.
      [1913 Webster]

   2. Belonging to the natural or essential constitution;
      peculiar; not common; particular; as, every animal has his
      proper instincts and appetites.
      [1913 Webster]

            Those high and peculiar attributes . . . which
            constitute our proper humanity.       --Coleridge.
      [1913 Webster]

   3. Befitting one's nature, qualities, etc.; suitable in all
      respect; appropriate; right; fit; decent; as, water is the
      proper element for fish; a proper dress.
      [1913 Webster]

            The proper study of mankind is man.   --Pope.
      [1913 Webster]

            In Athens all was pleasure, mirth, and play,
            All proper to the spring, and sprightly May.
                                                  --Dryden.
      [1913 Webster]

   4. Becoming in appearance; well formed; handsome. [Archaic]
      "Thou art a proper man." --Chaucer.
      [1913 Webster]

            Moses . . . was hid three months of his parents,
            because they saw he was a proper child. --Heb. xi.
                                                  23.
      [1913 Webster]

   5. Pertaining to one of a species, but not common to the
      whole; not appellative; -- opposed to common; as, a
      proper name; Dublin is the proper name of a city.
      [1913 Webster]

   6. Rightly so called; strictly considered; as, Greece proper;
      the garden proper.
      [1913 Webster]

   7. (Her.) Represented in its natural color; -- said of any
      object used as a charge.
      [1913 Webster]

   In proper, individually; privately. [Obs.] --Jer. Taylor.


   Proper flower or Proper corolla (Bot.), one of the single
      florets, or corollets, in an aggregate or compound flower.


   Proper fraction (Arith.) a fraction in which the numerator
      is less than the denominator.

   Proper nectary (Bot.), a nectary separate from the petals
      and other parts of the flower. -- Proper noun (Gram.), a
      name belonging to an individual, by which it is
      distinguished from others of the same class; -- opposed to
      common noun; as, John, Boston, America.

   Proper perianth or Proper involucre (Bot.), that which
      incloses only a single flower.

   Proper receptacle (Bot.), a receptacle which supports only
      a single flower or fructification.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Proper \Prop"er\, adv.
   Properly; hence, to a great degree; very; as, proper good.
   [Colloq & Vulgar]
   [1913 Webster]

WordNet (r) 3.0 (2006):

proper
    adj 1: marked by suitability or rightness or appropriateness;
           "proper medical treatment"; "proper manners" [ant:
           improper]
    2: having all the qualities typical of the thing specified;
       "wanted a proper dinner; not just a snack"; "he finally has a
       proper job"
    3: limited to the thing specified; "the city proper"; "his claim
       is connected with the deed proper"
    4: appropriate for a condition or purpose or occasion or a
       person's character, needs; "everything in its proper place";
       "the right man for the job"; "she is not suitable for the
       position" [syn: proper, right]

Moby Thesaurus II by Grady Ward, 1.0:

274 Moby Thesaurus words for "proper":
   Christian, OK, absolute, accepted, accommodated to, according to,
   according to Hoyle, accurate, acknowledged, adapted, adapted to,
   adjusted to, admitted, advantageous, advisable, after,
   agreeable to, agreeably to, all right, alone, answerable to,
   applicable, apposite, appropriate, approved, apropos, apt, arrant,
   au fait, authentic, authoritative, balanced, banausic, becoming,
   befitting, being done, beneficial, blamed, by, canonical, capable,
   characteristic, civil, classical, comely, comme il faut,
   commodious, competent, complete, condign, conformable,
   conformable to, conforming, conformist, confounded, congruent with,
   congruous, consistent with, consummate, convenient, conventional,
   correct, crashing, crass, customary, de rigueur, dead right,
   decent, decided, decorous, defensible, definitive, delicate,
   deserved, desirable, desired, diagnostic, dignified, distinct,
   distinctive, distinguished, downright, due, egregious, elegant,
   employable, equitable, established, evangelical, even, evenhanded,
   exact, expected, expedient, fair, fair and square, faithful,
   faultless, favorable, feasible, felicitous, firm, fit, fitten,
   fitting, flagrant, flawless, formal, fructuous, functional,
   genteel, gentlemanly, glaring, good, good for, gross, happy,
   helpful, idiocratic, idiosyncratic, in accordance with,
   in agreement with, in character, in compliance with,
   in conformity with, in correspondence to, in harmony with,
   in keeping with, in line with, in lock-step with, in obedience to,
   in step with, in uniformity with, individual, infernal, inspired,
   intolerable, intrinsic, just, just right, justifiable, justified,
   kosher, ladylike, lawful, legal, letter-perfect, level, likely,
   literal, marked, meet, meet and right, merited, meticulous, modest,
   nice, normal, normative, of general utility, of help, of service,
   of the faith, of use, okay, only, opportune, orthodox,
   orthodoxical, out-and-out, outright, own, particular, peculiar,
   per, perfect, polite, politic, positive, practical, pragmatical,
   precious, precise, prig, priggish, prissy, profitable, profound,
   pronounced, proper to, prudish, punctilious, puritanical,
   qualified, quintessential, rank, received, recognized,
   recommendable, refined, regular, respectable, respective, right,
   right and proper, righteous, rightful, rigorous, satisfactory,
   scriptural, seasonable, seemly, sensible, separate, serviceable,
   shattering, shocking, single, singular, solely, sortable, sound,
   special, specific, square, standard, stark, stark-staring,
   straight, straight-up-and-down, straitlaced, strictly speaking,
   stuffy, suitable, suitable for, suited, superlative, surpassing,
   textual, the veriest, thorough, thoroughgoing, timely,
   to be desired, total, traditional, traditionalistic, true,
   true to form, true-blue, unbearable, unconscionable, undeniable,
   unequivocal, uniform with, unique, unmitigated, unqualified,
   unrelieved, unspoiled, urbane, useful, usual, utilitarian, utter,
   warrantable, warranted, well-chosen, well-expressed, well-put,
   well-timed, wicked, wise, worthwhile



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

PROPER. That which is essential, suitable, adapted, and correct.
     2. Congress is authorized by art, 1, s. 8, of the constitution of the
United States, "to make all laws which shall be necessary and proper, for
carrying into execution the foregoing powers, and all other powers vested by
this constitution of the United States, in any department. or officer
thereof." See Necessary and Proper.