Callous

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late Middle English (in the Latin sense): from Latin callosus ‘hard-skinned’.

wiktionary

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From Latin callōsus(“hard-skinned”), from callum(“hardened skin”) + -ōsus.

etymonline

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callous (adj.)

c. 1400, "hardened," in the physical sense, from Latin callosus "thick-skinned," from callus, callum "hard skin" (see callus). The figurative sense of "unfeeling, hardened in the mind" appeared in English by 1670s. Related: Callously; callousness.