1610s (implied in dissociated), from Latin dissociatus, past participle of dissociare "to separate from companionship, disunite, set at variance," from dis- "apart" (see dis-) + sociare "to join," from socius "companion" (see social (adj.)). Attested from 1540s as a past participle adjective meaning "separated."[dissociate etymology, dissociate origin, 英语词源]