1. An agent, such as yeast, that causes batter or dough to rise, especially by fermentation.
2. An element, influence, or agent that works subtly to lighten, enliven, or modify a whole.
tr.v. leav·ened, leav·en·ing, leav·ens
1. To add a rising agent to.
2. To cause to rise, especially by fermentation.
3. To pervade with a lightening, enlivening, or modifying influence.
[Middle English, from Old French levain, from Vulgar Latin *levāmen, from Latin levāre, to raise; see legwh- in the Appendix of Indo-European roots.]
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