Yours, Etc.: Origins and Uses of 8 Sign-Offs
1520s, from Middle French incinération (14c.), from Medieval Latin incinerationem (nominative incineratio), noun of action from past participle stem of incinerare (see incinerate).
1550s, from Medieval Latin incineratus "reduced to ashes," pp. of incinerare, from Latin in- "into" (see in- (2)) + cinis (genitive cineris) "ashes," from PIE root *keni- "dust, ashes" (cf. Greek konis "dust"). Used earlier in English as a past participle adjective meaning "reduced to ashes" (early 15c.). Related: Incinerated; incinerating.