late 14c., originally of planets, from Old French conjonction "union, joining, sexual intercourse" (12c.), from Latin coniunctionem (nominative coniunctio), from past participle stem of coniugare "join together" (see conjugal). Cf. Italian congiunzione, Spanish conjunción. Grammatical sense (late 14c.) was in Latin, a loan-translation of Greek syndesmos. The word also had the meaning "sexual union" 17c.-18c.