1560s "to separate, cause to be disjoined" (implied in disunited); see dis- + unite. Possibly from Late Latin disunitus, past participle of disunire. Intransitive meaning "to part, fall asunder, become divided" is from 1670s. Related: Disuniting.
distrustful
disturb
disturbance
disturbed
disunion
disunite
disunity
disuse
disused
ditch
ditheism