1590s, from Latin innocuus "harmless," from in- "not" (see in- (1)) + nocuus "hurtful," from root of nocere "to injure, harm," from *nok-s-, suffixed form of PIE root *nek- (1) "death" (see necro-). Related: Innocuously; innocuousness.[innocuous etymology, innocuous origin, 英语词源]