n. [ OE. levain, levein, F. levain, L. levamen alleviation, mitigation; but taken in the sense of, a raising, that which raises, fr. levare to raise. See Lever, n. ] 1. Any substance that produces, or is designed to produce, fermentation, as in dough or liquids; esp., a portion of fermenting dough, which, mixed with a larger quantity of dough, produces a general change in the mass, and renders it light; yeast; barm. [ 1913 Webster ]

2. Anything which makes a general assimilating (especially a corrupting) change in the mass. [ 1913 Webster ]

Beware of the leaven of the Pharisees, which is hypocrisy. Luke xii. 1. [ 1913 Webster ]

v. t. [ imp. & p. p. Leavened p. pr. & vb. n. Leavening ] 1. To make light by the action of leaven; to cause to ferment. [ 1913 Webster ]

A little leaven leaveneth the whole lump. 1 Cor. v. 6. [ 1913 Webster ]

2. To imbue; to infect; to vitiate. [ 1913 Webster ]

With these and the like deceivable doctrines, he leavens also his prayer. Milton. [ 1913 Webster ]

adj. made light by aerating, as with yeast or baking powder. Opposite of unleavened. [ Narrower terms: sourdough(prenominal) ] [ WordNet 1.5 ]

n. 1. The act of making light, or causing to ferment, by means of leaven. [ 1913 Webster ]

2. That which leavens or makes light. Bacon. [ 1913 Webster ]

a. Containing leaven. Milton. [ 1913 Webster ]