The Collaborative International Dictionary of English v.0.48:

Classify \Clas"si*fy\, v. t. [imp. & p. p. Classified; p. pr.
   & vb. n. Classifying.] [L. classis class + -fy.]
   To distribute into classes; to arrange according to a system;
   to arrange in sets according to some method founded on common
   properties or characters.

   Syn: To arrange; distribute; rank.
        [1913 Webster]

WordNet (r) 3.0 (2006):

classify
    v 1: arrange or order by classes or categories; "How would you
         classify these pottery shards--are they prehistoric?" [syn:
         classify, class, sort, assort, sort out,
         separate]
    2: declare unavailable, as for security reasons; "Classify these
       documents" [ant: declassify]
    3: assign to a class or kind; "How should algae be classified?";
       "People argue about how to relegate certain mushrooms" [syn:
       relegate, classify]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "classify":
   alphabetize, analyze, appraise, arrange, assess, assort, bolt,
   bosom, break down, catalog, categorize, class, codify, collate,
   conceal, digest, divide, evaluate, factor, file, file and forget,
   gauge, gradate, grade, group, hold out on, identify, in petto,
   index, keep, keep back, keep between us, keep buttoned up,
   keep close, keep dark, keep from, keep in ignorance, keep mum,
   keep secret, keep snug, keep under wraps, list, make no sign,
   never let on, not give away, not tell, order, pigeonhole, place,
   play dumb, range, rank, rate, riddle, screen, secrete, separate,
   sieve, sift, size, sort, sort out, subdivide, subordinate,
   tabulate, thrash out, type, veil, weigh, winnow, withhold