The Collaborative International Dictionary of English v.0.48:

Crass \Crass\ (kr?s), a. [L. crassus thick, fat, gross, prob.
   orig., closely woven. See Grease animal fat, and cf.
   Crate, Hurdle.]
   Gross; thick; dense; coarse; not elaborated or refined.
   "Crass and fumid exhalations." --Sir. T. Browne. "Crass
   ignorance" --Cudworth.
   [1913 Webster] Crassament

WordNet (r) 3.0 (2006):

crass
    adj 1: (of persons) so unrefined as to be lacking in
           discrimination and sensibility