leaven /ˈlɛv.ən/verb 5noun 3forms 5phrases 1 verb5 •To add a leavening agent.Yeast is used to leaven bread, making it rise during baking. •(figurative) To temper an action, decision, attitude, characteristic, etc.Duke. No more euasion: We haue with a leauen'd, and prepared choice Proceeded to you; therefore take your honors:[...] — 1603 •(figurative) To imbue; to infect; to vitiate.The comedian's jokes helped leaven the atmosphere during the serious meeting.Her optimism seemed to leaven the otherwise tense environment. •To cause to rise by fermentation. •To rise or become larger; to prove. noun3 •Any agent used to make dough rise or to have a similar effect on baked goods. •(figurative) Anything that induces change, especially a corrupting or vitiating change.Take heed, beware of the leaven of the Pharisees, and of the leaven of Herod. — 1611 •(Judaism) Chametz.On the fourteenth day of Nisan men search for leaven by candlelight. — 1878 formsleavened · leavening · leaveneth · leavens · leavenest Phrases with leaven of the same leavenOf a kind, cut from the same cloth.