The Collaborative International Dictionary of English v.0.48:

Dandruff \Dandruff\ (d[a^]n"dr[u^]f), n. [Prob. from W.
   toncrust, peel, skin + AS. dr[=o]f dirty, draffy, or W. drwg
   bad: cf. AS. tan a letter, an eruption. [root]240.]
   A scurf which forms on the head, and comes off in small
   scales or particles. [Written also dandriff.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

dandruff
    n 1: a condition in which white scales of dead skin are shed by
         the scalp
    2: loose scales shed from the scalp; "I could see the dandruff
       on her shoulders"

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "dandruff":
   carrion, chip, corruption, decay, excrement, filth, flake,
   floccule, flocculus, flock, foul matter, furfur, gangrene, mess,
   muck, mucus, obscenity, ordure, paring, pus, putrid matter, rot,
   scale, scurf, scuz, shaving, slime, smut, snot, sordes