Entry 1 sense Webster, 1913 Reasoner /(rē"z'n*ẽr)/ · Rea·son·er · IPA /rˈiːzənər/ 01 n. One who reasons or argues; as, a fair reasoner; a close reasoner; a logical reasoner. 1. One who reasons or argues; as, a fair reasoner; a close reasoner; a logical reasoner.