The Collaborative International Dictionary of English v.0.48:

Presumption \Pre*sump"tion\ (?; 215), n. [L. praesumptio: cf. F.
   pr['e]somption, OF. also presumpcion. See Presume.]
   1. The act of presuming, or believing upon probable evidence;
      the act of assuming or taking for granted; belief upon
      incomplete proof.
      [1913 Webster]

   2. Ground for presuming; evidence probable, but not
      conclusive; strong probability; reasonable supposition;
      as, the presumption is that an event has taken place.
      [1913 Webster]

   3. That which is presumed or assumed; that which is supposed
      or believed to be real or true, on evidence that is
      probable but not conclusive. "In contradiction to these
      very plausible presumptions." --De Quincey.
      [1913 Webster]

   4. The act of venturing beyond due beyond due bounds; an
      overstepping of the bounds of reverence, respect, or
      courtesy; forward, overconfident, or arrogant opinion or
      conduct; presumptuousness; arrogance; effrontery.
      [1913 Webster]

            Thy son I killed for his presumption. --Shak.
      [1913 Webster]

            I had the presumption to dedicate to you a very
            unfinished piece.                     --Dryden.
      [1913 Webster]

   Conclusive presumption. See under Conclusive.

   Presumption of fact (Law), an argument of a fact from a
      fact; an inference as to the existence of one fact not
      certainly known, from the existence of some other fact
      known or proved, founded on a previous experience of their
      connection; supposition of the truth or real existence of
      something, without direct or positive proof of the fact,
      but grounded on circumstantial or probable evidence which
      entitles it to belief. --Burrill. --Best. --Wharton.

   Presumption of law (Law), a postulate applied in advance to
      all cases of a particular class; e. g., the presumption of
      innocence and of regularity of records. Such a presumption
      is rebuttable or irrebuttable.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

235 Moby Thesaurus words for "presumption":
   adventurousness, allegory, allusion, apriorism, aptitude,
   arcane meaning, arrogance, aspiration, assumption, assurance,
   assured faith, attitude, audaciousness, audacity, axiom, basis,
   belief, bias, boldness, brashness, brass, brazenness, brinkmanship,
   bumptiousness, butting-in, chance, cheek, cheekiness,
   cheerful expectation, chutzpah, climate of opinion, coloration,
   common belief, community sentiment, conceit, concept, conception,
   conclusion, confidence, conjecture, connotation, consensus gentium,
   consideration, contumely, conviction, courage fou,
   courting disaster, crust, daredevilry, daredeviltry, daring,
   deduction, dependence, desire, doomed hope, effrontery, entailment,
   estimate, estimation, ethos, evidence, expectation, eye, face,
   fair expectation, fair prospect, faith, familiarity,
   favorable prospect, feasibility, feeling, fervent hope,
   fire-eating, flirting with death, foolhardiness, forejudgment,
   forwardness, gall, general belief, going for broke, good chance,
   good cheer, good hope, great expectations, grounds, guess,
   guesswork, hardihood, harebrainedness, high hopes, hint, hope,
   hopeful prognosis, hopefulness, hopes, hoping, hoping against hope,
   hubris, hypothesis, idea, immodesty, impertinence, implication,
   implied meaning, import, imposition, impression, impudence,
   inference, innuendo, inquisitiveness, insolence, intermeddling,
   intimation, intrusiveness, involvement, ironic suggestion,
   judgment, lawlessness, liability, liberties, liberty abused,
   license, licentiousness, lights, likelihood, likeliness, meaning,
   meddlesomeness, meddling, metaphorical sense, mind, mystique,
   nerve, notion, nuance, observation, obtrusiveness, occult meaning,
   odds, officiousness, opinion, outlook, overconfidence, overtone,
   overweening, overweeningness, parti pris, personal judgment,
   plausibility, playing with fire, point of view, popular belief,
   posit, position, postulate, postulation, postulatum, posture,
   prayerful hope, preapprehension, preconception, preconclusion,
   preconsideration, predecision, predetermination, predilection,
   predisposition, prejudgment, prejudication, prejudice,
   premature judgment, premise, premiss, prenotion, prepossession,
   presumptive evidence, presumptuousness, presupposal,
   presupposition, presurmise, prevailing belief, pride, probabilism,
   probability, procacity, promise, proposition, prospect, prospects,
   public belief, public opinion, pushiness, reaction, reason,
   reasonable ground, reasonable hope, reliance, sanguine expectation,
   security, sentiment, set of postulates, sight, stance, stand,
   subsense, subsidiary sense, subsumption, suggestion, supposal,
   supposing, supposition, surmise, suspicion, symbolism, temerity,
   tendency, theory, thesis, thinking, thought, tinge, touch, trust,
   undercurrent, undermeaning, undertone, undue liberty, uppishness,
   uppityness, verisimilitude, view, way of thinking,
   well-grounded hope, working hypothesis