callous (adj.)youdaoicibaDictYouDict[callous 词源字典]
c. 1400, "hardened," in the physical sense, from Latin callosus "thick-skinned," from callus, callum "hard skin" (see callus). The figurative sense of "unfeeling" appeared in English by 1670s. Related: Callously; callousness.[callous etymology, callous origin, 英语词源]