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.
The position of two celestial bodies when they have the same celestial longitude, especially a configuration in which a planet or the Moon lies on a straight line from Earth to or through the Sun. Planets in this position are not visible to the naked eye because they are in line with the Sun and obscured by its glare; the Moon in this position is new. ◇ The inner planets Mercury and Venus have two conjunction points with Earth. Either planet is at inferior conjunction when it lies directly between the Earth and the Sun, and is at superior conjunction when it lies directly opposite Earth on the far side of the Sun. The outer planets have only one conjunction point with Earth, when they lie opposite Earth on the far side of the Sun. Compare opposition. See more at elongation.
A word that joins words or groups of words. There are three kinds of conjunctions: coordinating, correlative, and subordinating. Coordinating conjunctions include and, but, or, not, yet, for, and so. Correlative conjunctions include the words in the pairs either/or, both/and, and neither/nor. Subordinating conjunctions begin subordinate clauses (see subordination) and join them to the rest of the sentence: “She didn't learn the real reason until she left the valley.”