Meaning

noun an organization of employees formed to bargain with the employer

noun the United States (especially the northern states during the American Civil War)

noun the act of pairing a male and female for reproductive purposes

originFrom Middle English unyoun, from Old French union, from Late Latin ūniō, ūniōnem (“oneness, unity”), from Latin ūnus (“one”). Doublet of unio.

Etymology from Wiktionary, CC BY-SA 3.0