c.1300, from stem of Old French joindre "join, connect, unite; have sexual intercourse with" (12c.), from Latin iungere "to join together, unite, yoke," from PIE *yeug- "to join, unite" (see jugular). Related: Joined; joining. In Middle English, join sometimes is short for enjoin. Join up "enlist in the army" is from 1916. Phrase if you can't beat them, join them is from 1953. To be joined at the hip figuratively ("always in close connection") is by 1986, from the literal sense in reference to "Siamese twins."