The Collaborative International Dictionary of English v.0.48:

Assumption \As*sump"tion\ (?; 215), n. [OE. assumpcioun a taking
   up into heaven, L. assumptio a taking, fr. assumere: cf. F.
   assomption. See Assume.]
   1. The act of assuming, or taking to or upon one's self; the
      act of taking up or adopting.
      [1913 Webster]

            The assumption of authority.          --Whewell.
      [1913 Webster]

   2. The act of taking for granted, or supposing a thing
      without proof; supposition; unwarrantable claim.
      [1913 Webster]

            This gives no sanction to the unwarrantable
            assumption that the soul sleeps from the period of
            death to the resurrection of the body. --Thodey.
      [1913 Webster]

            That calm assumption of the virtues.  --W. Black.
      [1913 Webster]

   3. The thing supposed; a postulate, or proposition assumed; a
      supposition.
      [1913 Webster]

            Hold! says the Stoic; your assumption's wrong.
                                                  --Dryden.
      [1913 Webster]

   4. (Logic) The minor or second proposition in a categorical
      syllogism.
      [1913 Webster]

   5. The taking of a person up into heaven. Hence: (Rom. Cath.
      & Greek Churches) A festival in honor of the ascent of the
      Virgin Mary into heaven.
      [1913 Webster]

WordNet (r) 3.0 (2006):

assumption
    n 1: a statement that is assumed to be true and from which a
         conclusion can be drawn; "on the assumption that he has
         been injured we can infer that he will not to play" [syn:
         premise, premiss, assumption]
    2: a hypothesis that is taken for granted; "any society is built
       upon certain assumptions" [syn: assumption, supposition,
       supposal]
    3: the act of taking possession of or power over something; "his
       assumption of office coincided with the trouble in Cuba";
       "the Nazi assumption of power in 1934"; "he acquired all the
       company's assets for ten million dollars and the assumption
       of the company's debts" [syn: assumption, laying claim]
    4: celebration in the Roman Catholic Church of the Virgin Mary's
       being taken up into heaven when her earthly life ended;
       corresponds to the Dormition in the Eastern Orthodox Church
       [syn: Assumption, Assumption of Mary, August 15]
    5: (Christianity) the taking up of the body and soul of the
       Virgin Mary when her earthly life had ended
    6: audacious (even arrogant) behavior that you have no right to;
       "he despised them for their presumptuousness" [syn:
       presumption, presumptuousness, effrontery,
       assumption]
    7: the act of assuming or taking for granted; "your assumption
       that I would agree was unwarranted"

Moby Thesaurus II by Grady Ward, 1.0:

281 Moby Thesaurus words for "assumption":
   a priori principle, about-face, acceptance, accession, acquisition,
   admission, admittance, adoption, affirmation, alchemy, allegory,
   allusion, anointing, anointment, apotheosis, appointment,
   appropriation, apriorism, arcane meaning, arrogation, ascension,
   ascent, aspiration, assertion, assignment, assimilation,
   assumed position, assumption, assurance, assured faith, attitude,
   authorization, axiom, basis, beatification, becoming,
   borrowed plumes, canonization, categorical proposition, change,
   change-over, cheerful expectation, climate of opinion,
   colonization, coloration, common belief, community sentiment,
   conceit, concept, conception, conclusion, confidence, conjecture,
   connotation, conquest, consecration, consensus gentium,
   consideration, conversion, conviction, copying, coronation, data,
   deification, delegation, dependence, deputation, derivation,
   deriving, desire, doomed hope, election, elevation, empowerment,
   encroachment, enshrinement, enslavement, entailment, erection,
   escalation, estimate, estimation, ethos, exaltation, expectation,
   eye, fair prospect, faith, familiarity, feeling, fervent hope,
   first principles, flip-flop, foundation, fundamental, gathering,
   general belief, getting, good cheer, good hope, great expectations,
   ground, growth, guess, guesswork, height, high hopes, hint, hope,
   hopeful prognosis, hopefulness, hopes, hoping, hoping against hope,
   hubris, hypothesis, hypothesis ad hoc, idea, imitation,
   implication, implied meaning, import, imposition, impression,
   indent, inference, infringement, innuendo, insolence, intimation,
   invasion, involvement, ironic suggestion, judgment, lapse, law,
   lawlessness, legitimate succession, lemma, liberties,
   liberty abused, license, licentiousness, lifting, lights,
   major premise, meaning, metaphorical sense, mind, minor premise,
   mocking, mystique, naturalization, notion, nuance, observation,
   occult meaning, occupation, opinion, overtone, overweening,
   overweeningness, passage, pasticcio, pastiche, personal judgment,
   philosopheme, philosophical proposition, pirating, plagiarism,
   plagiary, playing God, point of view, popular belief, posit,
   position, postulate, postulation, postulatum, posture,
   prayerful hope, preemption, premise, preoccupation, prepossession,
   presumption, presumptuousness, presupposal, presupposition,
   prevailing belief, principle, progress, promise, proposition,
   propositional function, prospect, prospects, public belief,
   public opinion, raising, re-formation, reaction, rearing, receipt,
   receival, receiving, reception, reconversion, reduction, reliance,
   requisition, resolution, resurrection, reversal,
   sanguine expectation, security, seizure, sentiment,
   set of postulates, shift, sight, simulation, stance, statement,
   subjugation, subsense, subsidiary sense, subsumption, succession,
   suggestion, sumption, supposal, supposing, supposition, surmise,
   sursum corda, switch, switch-over, symbolism, takeover, taking,
   taking over, the Ascension, the Assumption, theorem, theory,
   thesis, thinking, thought, tinge, touch, transformation, transit,
   transition, translation, trespass, trespassing, trust, truth table,
   truth-function, truth-value, turning into, undercurrent,
   undermeaning, undertone, undue liberty, upbuoying, upcast,
   upheaval, uplift, uplifting, upping, uprearing, upthrow, upthrust,
   usurpation, view, volte-face, way of thinking, well-grounded hope,
   working hypothesis



U.S. Gazetteer Counties (2000):

Assumption -- U.S. Parish in Louisiana
   Population (2000):    23388
   Housing Units (2000): 9635
   Land area (2000):     338.681886 sq. miles (877.182021 sq. km)
   Water area (2000):    25.871397 sq. miles (67.006609 sq. km)
   Total area (2000):    364.553283 sq. miles (944.188630 sq. km)
   Located within:       Louisiana (LA), FIPS 22
   Location:             29.926900 N, 91.054794 W
   Headwords:
    Assumption
    Assumption, LA
    Assumption Parish
    Assumption Parish, LA


U.S. Gazetteer Places (2000):

Assumption, IL -- U.S. city in Illinois
   Population (2000):    1261
   Housing Units (2000): 607
   Land area (2000):     0.879889 sq. miles (2.278902 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.879889 sq. miles (2.278902 sq. km)
   FIPS code:            02609
   Located within:       Illinois (IL), FIPS 17
   Location:             39.519545 N, 89.049129 W
   ZIP Codes (1990):     62510
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Assumption, IL
    Assumption