leaven
/ˈlevn; `lɛvən/ n[U]
1 substance (eg yeast) used to make dough rise before it is baked to make bread 酵母; 面肥.
2 (fig 比喻) quality or influence that makes people, an atmosphere, etc less serious, more lively, etc 使人、 气氛等轻松、 活跃等的因素
a lively artistic community, acting as the leaven in society 给社会增加生气的活跃的艺术团体. leaven, v [Tn]
1 add leaven to (sth) 在（某物）中加酵母
leavened bread 发酵面包.
2 (fig 比喻) enliven (sth) 使（某事物）活跃.