id (n.) Look up id at Dictionary.com
1924, in Joan Riviere's translation of Freud's "Das Ich und das Es" (1923), from Latin id "it" (as a translation of German es "it" in Freud's title), used in psychoanalytical theory to denote the unconscious instinctual force. Latin id is from PIE pronominal stem *i- (see yon).