- 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. - Anything which makes a general assimilating (especially a
corrupting) change in the mass.
2 . Leaven
[ v. t.]
- To make light by the action of leaven; to cause to
ferment. - To imbue; to infect; to vitiate.
Meaning of 'leaven' (Princeton's WordNet)
1 . leaven
[ n]
Meaning (1): - an influence that works subtly to lighten or modify something