The Collaborative International Dictionary of English v.0.48:

Proposition \Prop`o*si"tion\, n. [L. propositio: cf. F.
   proposition. See Propound.]
   1. The act of setting or placing before; the act of offering.
      "Oblations for the altar of proposition." --Jer. Taylor.
      [1913 Webster]

   2. That which is proposed; that which is offered, as for
      consideration, acceptance, or adoption; a proposal; as,
      the enemy made propositions of peace; his proposition was
      not accepted.
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   3. A statement of religious doctrine; an article of faith;
      creed; as, the propositions of Wyclif and Huss.
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            Some persons . . . change their propositions
            according as their temporal necessities or
            advantages do turn.                   --Jer. Taylor.
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   4. (Gram. & Logic) A complete sentence, or part of a sentence
      consisting of a subject and predicate united by a copula;
      a thought expressed or propounded in language; a from of
      speech in which a predicate is affirmed or denied of a
      subject; as, snow is white.
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   5. (Math.) A statement in terms of a truth to be
      demonstrated, or of an operation to be performed.
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   Note: It is called a theorem when it is something to be
         proved, and a problem when it is something to be done.
         [1913 Webster]

   6. (Rhet.) That which is offered or affirmed as the subject
      of the discourse; anything stated or affirmed for
      discussion or illustration.
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   7. (Poetry) The part of a poem in which the author states the
      subject or matter of it.
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   Leaves of proposition (Jewish Antiq.), the showbread.
      --Wyclif (Luke vi. 4).
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   Syn: Proposal; offer; statement; declaration.

   Usage: Proposition, Proposal. These words are both from
          the Latin verb proponere, to set forth, and as here
          compared they mark different forms or stages of a
          negotiation. A proposition is something presented for
          discussion or consideration; as, propositions of
          peace. A proposal is some definite thing offered by
          one party to be accepted or rejected by the other. If
          the proposition is favorably received, it is usually
          followed by proposals which complete the arrangement.
          [1913 Webster]

WordNet (r) 3.0 (2006):

proposition
    n 1: (logic) a statement that affirms or denies something and is
         either true or false
    2: a proposal offered for acceptance or rejection; "it was a
       suggestion we couldn't refuse" [syn: suggestion,
       proposition, proffer]
    3: an offer for a private bargain (especially a request for
       sexual favors)
    4: the act of making a proposal; "they listened to her proposal"
       [syn: proposal, proposition]
    5: a task to be dealt with; "securing adequate funding is a
       time-consuming proposition"
    v 1: suggest sex to; "She was propositioned by a stranger at the
         party"

Moby Thesaurus II by Grady Ward, 1.0:

162 Moby Thesaurus words for "proposition":
   a priori principle, a priori truth, accost, advance, affair,
   affirmance, affirmation, allegation, announcement, annunciation,
   approach, apriorism, assertion, asseveration, assumed position,
   assumption, attempt, averment, avouchment, avowal, axiom, basis,
   bring before, bring forward, bring up, broach, brocard, business,
   categorical proposition, commend to attention, commitment,
   conclusion, conjecture, contract, creed, data, deal, declaration,
   dictate, dictum, effort, engagement, enterprise, enunciation,
   first principles, formula, foundation, game plan, golden rule,
   ground, guesswork, hypothesis, hypothesis ad hoc, importune,
   improper suggestion, indecent proposal, inference, instance,
   introduce, invitation, ipse dixit, launch, law, lay before, lemma,
   major premise, make a motion, make a pass, make advances,
   make an overture, manifesto, minor premise, moot, motion, move,
   obligation, offer a resolution, open up, operation, overture, pass,
   philosopheme, philosophical proposition, plan, pose, position,
   position paper, positive declaration, postulate, postulation,
   postulatum, predicate, predication, prefer, premise, presumption,
   presupposal, presupposition, principium, principle, proclamation,
   profession, proffer, program, project, projection, pronouncement,
   proposal, propose, propositional function, propound, prospectus,
   protest, protestation, put, put forth, put forward, put it to,
   recommend, request, resolution, rule, say, say-so, saying,
   scenario, self-evident truth, set before, set forth,
   set of postulates, settled principle, sexual advance, solicit,
   stance, stand, start, statement, submit, suggest, suggestion,
   sumption, supposal, supposing, supposition, surmise, task, theorem,
   thesis, throw a pass, truism, truth, truth table, truth-function,
   truth-value, undertaking, universal truth, utterance, venture,
   vouch, word, work, working hypothesis



The Free On-line Dictionary of Computing (30 December 2018):

proposition

    A statement in propositional logic which may be
   either true or false.  Each proposition is typically
   represented by a letter in a formula such as "p => q",
   meaning proposition p implies proposition q.

   (2006-03-14)


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

PROPOSITION. An offer to do something. Until it has been accepted, a
proposition may be withdrawn by the party who makes it; and to be binding,
the acceptance must be in the same terms, without any variation. Vide
Acceptance; Offer; To retract; and 1 L. R. 190; 4 L. R. 80.