The Collaborative International Dictionary of English v.0.48:

Diversify \Di*ver"si*fy\, v. t. [imp. & p. p. Diversified; p.
   pr. & vb. n. Diversifying.] [F. diversifier, LL.
   diversificare, fr. L. diversus diverse + ficare (in comp.),
   akin to facere to make. See Diverse.]
   To make diverse or various in form or quality; to give
   variety to; to variegate; to distinguish by numerous
   differences or aspects.
   [1913 Webster]

         Separated and diversified on from another. --Locke.
   [1913 Webster]

         Its seven colors, that diversify all the face of
         nature.                                  --I. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diversify
    v 1: make (more) diverse; "diversify a course of study"
    2: spread into new habitats and produce variety or variegate;
       "The plants on this island diversified" [syn: diversify,
       radiate]
    3: vary in order to spread risk or to expand; "The company
       diversified" [syn: diversify, branch out, broaden]
       [ant: narrow, narrow down, specialise, specialize]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "diversify":
   accommodate, adapt, adjust, alter, ameliorate, analyze, anatomize,
   atomize, be changed, be converted into, be renewed, better,
   bottom out, branch out, break, break up, change, checker, chop,
   chop and change, chop logic, come about, come around, come round,
   convert, deform, degenerate, denature, desynonymize, deteriorate,
   deviate, differ, difference, differentiate, discriminate,
   disequalize, disjoin, dissent, distinguish, distribute, disunify,
   divaricate, diverge, divide, fit, flop, haul around, improve,
   individualize, individuate, jibe, make a distinction, mark,
   mark off, mark out, meliorate, mitigate, mix, modify, modulate,
   mutate, overthrow, particularize, personalize, qualify, re-create,
   realign, rebuild, reconstruct, redesign, refine a distinction,
   refit, reform, relieve, remake, renew, reshape, restructure,
   revamp, revive, ring changes, ring the changes, segregate,
   separate, set apart, set off, sever, severalize, shift,
   shift the scene, shuffle the cards, specialize, split hairs,
   spread, subvert, swerve, tack, take a turn, turn, turn aside,
   turn into, turn the corner, turn the scale, turn the tables,
   turn the tide, turn upside down, undergo a change, variate,
   variegate, vary, veer, warp, work a change, worsen