Question: what is the latin root of union?
Answer: from Late Latin unionem (nominative unio) "oneness, unity, a uniting," also in Latin meaning "a single pearl or onion," from unus "one," from PIE root *oi-no- "one, unique." Sense of "action of uniting into one political body" is attested from 1540s. Meaning "group of people or states" is from 1650s.