any of several small trees with aromatic leaves, especially the sweet bay, or bay laurel (Laurus nobilis), source of the bay leaf (q.v.) used in cooking. The California laurel (q.v.; Umbellularia californica) is an ornamental tree also called the bay tree. The bay rum tree, or simply bay (Pimenta racemosa), has leaves and twigs that yield, when distilled, oil of bay, which is used in perfumery and in the preparation of bay rum.