• (British, America) IPA: /ˈlɛv.ən/

leaven

1. Any agent used to make dough rise or to have a similar effect on baked goods.
2. (figurative) Anything that makes a general assimilating change in the mass.
   • 1611, The Holy Bible, […] (King James Version), imprinted at London: By Robert Barker, […], OCLC 964384981 ↗, Mark 8:15 ↗:

     Take heed, beware of the leaven of the Pharisees, and of the leaven of Herod

• (any agent used to make dough rise) leavening agent, raising agent

• French: levain, ferment
• German: Treibmittel, Triebmittel, Ferment
• Italian: lievito
• Portuguese: fermento, levedura
• Russian: заква́ска
• Spanish: levadura, polvos de hornear

leaven (leavens, present participle leavening; past and past participle leavened)

1. (transitive) To add a leavening agent.
2. (transitive) To cause to rise by fermentation.
3. (transitive, figuratively) To temper an action or decision.
   • 1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, →ISBN, page vii:

     With fresh material, taxonomic conclusions are leavened by recognition that the material examined reflects the site it occupied; a herbarium packet gives one only a small fraction of the data desirable for sound conclusions. Herbarium material does not, indeed, allow one to extrapolate safely: what you see is what you get{{...}

4. (transitive, figuratively) To imbue; to infect; to vitiate.
   • 1649, John Milton, Eikonoklastes, London: 1756, p. 30,

     With these and the like deceivable doctrines, he levens also his prayer.

   • 1716, Thomas Browne, Christian Morals, 2nd edition edited by Samuel Johnson, London: J. Payne, 1756, Part I, p. 7,

     […] pursue virtue virtuously: leven not good actions, nor render virtues disputable. Stain not fair acts with foul intentions […]

5. To rise or become larger.

• Italian: lievitare
• Spanish: leudar

• French: faire lever, faire fermenter
• Italian: lievitare
• Spanish: leudar