leaven
verb [ T ] uk/ˈlev.ən/ us/ˈlev.ən/
使发酵
to add a substance to bread or another food made with flour to make it increase in size when it is cooked
formal使变得有趣
to make something less boring
Even a speech on a serious subject should be leavened with a little humour. 即使是一篇题目很严肃的演讲也应该包含一些幽默的内容在里面。