n. 25B6; noun leaven is added to the dough : LEAVENING, fermentation agent, raising agent.
25B6; verb
yeast leavens the bread : RAISE, make rise, puff up, expand.
formal proceedings leavened by humour : PERMEATE, infuse, pervade, imbue, suffuse; enliven, liven up, invigorate, energize, electrify, ginger up, perk up, brighten up, season, spice; informal buck up, pep up.