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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- "death" (see necro-). Related: Innocuously; innocuousness.
innocuous in·noc·u·ous (ĭ-nŏk'yōō-əs)adj. Having no adverse effect; harmless.