1520s; see un- (1) "not" + righteous (adj.). In Middle English, the word was unrightwis, from Old English unrihtwis. Related: Unrighteously; unrighteousness.
an unrighteous man
an unrighteous law
unresponsive
unrest
unrestrained
unrestricted
unrewarded
unrighteous
unripe
unrivalled
unroll
unromantic
unruffled