mass noun
1- a substance, typically yeast, that is added to dough to make it ferment and rise酵素, 酵母。
1.1
- dough that is reserved from an earlier batch in order to start a later one fermenting面肥, 老面。
1.2
- figurative a pervasive influence that modifies something or transforms it for the better〈喻〉使全局改观（或改善）的影响：
they acted as an intellectual leaven to the warriors who dominated the city.
他们对主宰城市的武士们在智力方面起到了潜移默化的影响。
with obj.
1
- usu. as adj. leavened cause (dough or bread) to ferment and rise by adding leaven用酵母（或老面）使（面团, 面包）发酵：
leavened breads are forbidden during Passover.
逾越节期间禁吃发酵饼。
2
- permeate and modify or transform (something) for the better（使朝好的方向）改变：
the proceedings should be leavened by humour
会议的书面报告应当增添一点情趣
as noun leavening companies of Territorial Army volunteers with a leavening of regular soldiers.掺有正规军士兵的地方义勇军连队。
词源
Middle English: from Old French levain, based on Latin levamen 'relief' （literally 'means of raising'）， from levare to 'lift'.