leaven

From Middle English levayn, borrowed from Old French levain, from Vulgar Latin *levāmen, a noun based on Latin levō (“raise”).

• (Received Pronunciation, General American, Canada) IPA^(key): /ˈlɛv.ən/, [ˈlɛvn̩]

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• (General Australian, New Zealand) IPA^(key): /ˈlev.ən/, [ˈlevn̩]
• Rhymes: -ɛvən

leaven (countable and uncountable, plural leavens)

1. Any agent used to make dough rise or to have a similar effect on baked goods.
2. (figurative) Anything that induces change, especially a corrupting or vitiating change.
   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC, Mark 8:15:

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

   • 1834, L[etitia] E[lizabeth] L[andon], chapter XXXVI, in Francesca Carrara. […], volume III, London: Richard Bentley, […], (successor to Henry Colburn), →OCLC, page 299:

     On the far side was reflected a single red and meteoric cloud, which had treasured one last crimson ray from the sunset, or perhaps nursed within it the fiery leaven.

   • 1926, T.E. Lawrence, Seven Pillars of Wisdom, New York: Anchor, published 1991, page 213:

     The leaven of insincerity worked through all the fibres of his being.

3. Chametz.
   • 1878, “On The Passover”, in Joseph Barclay, transl., The Talmud, page 95:

     On the fourteenth day of Nisan men search for leaven by candlelight.

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

• (any agent used to make dough rise): agent, substance

• (any agent used to make dough rise): baking powder, yeast

leaven (third-person singular simple present leavens, present participle leavening, simple 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, decision, attitude, characteristic, etc.
   • c. 1603–1604 (date written), William Shakespeare, “Measure for Measure”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene i]:

     Duke. No more euasion:
     We haue with a leauen'd, and prepared choice
     Proceeded to you; therefore take your honors:[...]

   • 1920, Agatha Christie, The Mysterious Affair at Styles, London: Pan Books, published 1954, page 125:

     “A tinge of Jewish blood is not a bad thing. It leavens the”—she looked at him—“stolid stupidity of the ordinary Englishman.”

   • 1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, Chicago, Ill.: Field Museum of Natural History, →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^[1], London, published 1756, page 30:

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

   • 1716, Thomas Browne, edited by Samuel Johnson, Christian Morals‎^[2], 2nd edition, London: J. Payne, published 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; to prove. (Can we add an example for this sense?)

• leven (obsolete)

• yeast

From English leave +‎ -en.

leaven (third-person singular present leavt, past tense leavte, past participle geleaved or geleavt, auxiliary haben or sein)

1. (slang, gaming, otherwise rare) to leave

   Synonym: quitten

leaven

1. plural of leaf