Entry 2 senses · 2 variants Webster, 1913 Unreason · Un·rea·son · IPA n. v. t. 01 n. Want of reason; unreasonableness; absurdity. 1. Want of reason; unreasonableness; absurdity. Phrases & compounds Abbot of Unreason — See Abbot of Misrule, under Abbot. 02 v. t. To undo, disprove, or refute by reasoning. 1. To undo, disprove, or refute by reasoning.[Obs.] “To unreason the equity of God's proceedings.” — South.