The Collaborative International Dictionary of English v.0.48:

Simplify \Sim"pli*fy\, v. t. [imp. & p. p. Simplified; p. pr.
   & vb. n. Simplifying.] [Cf. F. simplifier, LL.
   simplificare. See Simple, and -fy.]
   To make simple; to make less complex; to make clear by giving
   the explanation for; to show an easier or shorter process for
   doing or making.
   [1913 Webster]

         The collection of duties is drawn to a point, and so
         far simplified.                          --A. Hamilton.
   [1913 Webster]

         It is important, in scientific pursuits, to be caitious
         in simplifying our deductions.           --W.
                                                  Nicholson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

simplify
    v 1: make simpler or easier or reduce in complexity or extent;
         "We had to simplify the instructions"; "this move will
         simplify our lives" [ant: complicate, perplex]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "simplify":
   abridge, account for, aid, allegorize, boil down, chasten, clarify,
   clean up, clear the way, clear up, compress, crack, curtail, cut,
   cut back, cut down, damp, dampen, decipher, decrease, deduct,
   deflate, demonstrate, demythologize, depreciate, depress, diminish,
   disentangle, disinvolve, distill, downgrade, ease, elucidate,
   enlighten, euhemerize, exemplify, expedite, explain, explain away,
   explicate, exposit, expound, facilitate, get across, get over,
   give reason for, give the meaning, grease, grease the ways,
   grease the wheels, hasten, help along, illuminate, illustrate,
   lessen, loose, lower, lubricate, make clear, make it clear,
   make plain, make way for, narrow, oil, open the way, open up,
   oversimplify, paraphrase, pare, pave the way, popularize,
   prepare the way, purify, put across, put over, quicken,
   rationalize, reduce, reduce to elements, refine, remove friction,
   restrain, retrench, roll back, run interference for, scale down,
   shed light upon, shorten, show, show how, show the way, smooth,
   smooth the way, soap the ways, solve, speed, spell out, step down,
   straighten, streamline, strip down, take from, throw light upon,
   tune down, unbar, unblock, unclog, unfold, unjam, unlock, unravel,
   untangle, vulgarize