"made into one," 1550s, past-participle adjective from unite (v.).
Entries linking to united
unite v.
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.