incessant (adj.)youdaoicibaDictYouDict[incessant 词源字典]
mid-15c., from Old French incessant (mid-14c.), from Late Latin incessantem (nominative incessans) "unceasing," from Latin in- "not" (see in- (1)) + cessantem (nominative cessans), present participle of cessare "cease" (see cease). Related: Incessantly (early 15c.).[incessant etymology, incessant origin, 英语词源]