[ 'lɛv(ə)n ]
■ noun
1》 a substance, typically yeast, added to dough to make it ferment and rise.
↘dough reserved from an earlier batch in order to start a later one fermenting.
2》 a pervasive influence that modifies something or transforms it for the better.
■ verb
1》 [usu. as adjective ~ed ] cause (dough or bread) to ferment and rise by adding ~.
2》 permeate and modify or transform for the better.
Origin
ME: from OFr. levain , based on L. levamen 'relief' (lit. 'means of raising'), from levare 'to lift'.