copula (n.)

early 15c., copulaten, "to join" (transitive), from Latin copulatus, past participle of copulare "join together, couple, bind, link, unite," from copula "band, tie, link," from PIE *ko-ap-, from *ko(m)- "together" (see com-) + *ap- (1) "to take, reach" (see apt). The intransitive sense of "unite sexually" is attested from 1630s. Related: Copulated; copulating.