leaven

Universal Words noun, verb noun [U] a substance, especially YEAST, that is added to bread before it is cooked to make it rise: (figurative) A few jokes add leaven to a boring speech. verb [VN] [oftenpassive] ~ sth (with sth) (formal) to make sth more interesting or cheerful by adding sth to it: Her speech was leavened with a touch of humour.