innocent: [14] Someone who is innocent is literally ‘harmless’. The word comes, partly via Old French, from Latin innocēns, an adjective formed with the negative prefix in- from the present participle of nocēre ‘harm’ (source of English nuisance) – hence, ‘not harming’. The slight semantic shift from ‘not harming’ to ‘blameless, guiltless’ took place in Latin. => nuisance
innocent (adj.)
mid-14c., "doing no evil, free from sin or guilt," from Old French inocent "harmless; not guilty; pure" (11c.), from Latin innocentem (nominative innocens) "not guilty, harmless, blameless," from in- "not" (see in- (1)) + nocentem (nominative nocens), present participle of nocere "to harm" (see noxious). Meaning "free from guilt of a specific crime or charge" is from late 14c. The earliest use was as a noun, "person who is innocent of sin or evil" (c. 1200). The Holy Innocents (early 14c.) were the young children slain by Herod after the birth of Jesus (Matt. ii:16).