Merriam-Webster's Collegiate® Dictionary, 11th Edition
CALLOUS
I. adjective
Etymology: Middle English, from Latin callosus, from callum, callus callous skin
Date: 15th century
1. being hardened and thickened, having calluses ,
2. feeling no emotion, feeling or showing no sympathy for others ; hard-hearted , callously adverb callousness noun
II. transitive verb
Date: 1834
to make callous