The Collaborative International Dictionary of English v.0.48:

Presuppose \Pre`sup*pose"\, v. t. [imp. & p. p. Presupposed;
   p. pr. & vb. n. Presupposing.] [Pref. pre- + suppose: cf.
   F. pr['e]supposer.]
   To suppose beforehand; to imply as antecedent; to take for
   granted; to assume; as, creation presupposes a creator.
   [1913 Webster]

         Each [kind of knowledge] presupposes many necessary
         things learned in other sciences, and known beforehand.
                                                  --Hooker.
   [1913 Webster]

WordNet (r) 3.0 (2006):

presuppose
    v 1: take for granted or as a given; suppose beforehand; "I
         presuppose that you have done your work" [syn:
         presuppose, suppose]
    2: require as a necessary antecedent or precondition; "This step
       presupposes two prior ones" [syn: presuppose, suppose]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "presuppose":
   affect, allegorize, allude to, assume, be afraid, be predisposed,
   believe, bring, bring to mind, call for, comprise, conceive,
   conclude, conjecture, connote, consider, contain, daresay, deduce,
   deem, divine, dream, entail, expect, fancy, feel, forejudge,
   gather, go off half-cocked, grant, guess, hint, imagine, implicate,
   imply, import, infer, insinuate, intimate, involve, judge,
   judge beforehand, jump the gun, lead to, let, let be, mean,
   mean to say, opine, point indirectly to, posit, postulate,
   preconceive, preconclude, predecide, predetermine, prefigure,
   prejudge, premise, presume, presurmise, provisionally accept,
   reckon, repute, require, say, subsume, suggest, suppose, surmise,
   suspect, take, take for, take for granted, take in, take it,
   take to be, think, understand