mid-14c., "irrational, illogical," from un- (1) "not" + reasonable. From late 14c. as "excessive, going beyond what is sensible or realistic." Related: Unreasonably; unreasonableness.
unready
unreal
unrealistic
unreality
unreason
unreasonable
unrecognizable
unreconciled
unreconstructed
unrecorded
unredeemed