Pronunciation: (kas'tur, kä'stur),[key] —n. 1. Also,castoreum.a brownish, unctuous substance with a strong, penetrating odor, secreted by certain glands in the groin of the beaver, used in medicine and perfumery.
2. a hat made of beaver or rabbit fur.
3. a heavy woolen cloth used mainly for coats.
4. a beaver.