Pronunciation: (mOOs),[key] —n. 1. Cookery. a. a sweetened dessert with whipped cream as a base, often stabilized with gelatin and chilled in a mold: chocolate mousse. b. an aspic, unsweetened and containing meat, vegetables, or fish: salmon mousse. 2. a foamy preparation used on the hair to help hold it in place, applied usually to damp hair before grooming or styling and worked in until absorbed.