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.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.