noun ·see caster, a small wheel.
2. castor ·noun a heavy quality of broadcloth for overcoats.
3. castor ·noun a hat, ·esp. one made of beaver fur; a beaver.
4. castor ·noun ·alt. of castorite.
5. castor ·noun castoreum. ·see castoreum.
6. castor ·noun a genus of rodents, including the beaver. ·see beaver.
7. castor ·noun the northernmost of the two bright stars in the constellation gemini, the other being pollux.