early 15c. (transitive), from Late Latin unitus, past participle of unire "to unite, make into one" (transitive), from Latin unus "one" (from PIE root *oi-no- "one, unique"). Intransitive sense from 1610s. Related: United; uniting.
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Definitions of united from WordNet
characterized by unity; being or joined into a single entity;
presented a united front
of or relating to two people who are married to each other;