Source : Webster's Revised Unabridged Dictionary (1913)

Coarsen \Coars"en\ (k[=o]rs"'n), v. t.
   To make coarse or vulgar; as, to coarsen one's character.
   [R.] --Graham.

Source : WordNet®

coarsen
     v 1: make or become coarse or coarser; "coarsen the surface";
          "Their minds coarsened"
     2: make less subtle or refined; "coarsen one's ideals"