Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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