Source : Webster's Revised Unabridged Dictionary (1913)

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.

            The assumption of authority.          --Whewell.

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

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

            That calm assumption of the virtues.  --W. Black.

   3. The thing supposed; a postulate, or proposition assumed; a
      supposition.

            Hold! says the Stoic; your assumption's wrong.
                                                  --Dryden.

   4. (Logic) The minor or second proposition in a categorical
      syllogism.

   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.

Source : WordNet®

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}]
     2: a hypothesis that is taken for granted; "any society is
        built upon certain assumptions" [syn: {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: {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 of Mary}, {August 15}]
     5: audacious (even arrogant) behavior that you have no right
        to; "he despised them for their presumptuousness" [syn: {presumption},
         {presumptuousness}, {effrontery}]
     6: (Christianity) the taking up of the body and soul of the
        Virgin Mary when her earthly life had ended
     7: the act of assuming or taking for granted; "your assumption
        that I would agree was unwarranted"