Definition of "Castor" :

noun: type genus of the Castoridae: beavers

noun: a hat made with the fur of a beaver (or similar material)

noun: a pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable

noun: a shaker with a perforated top for sprinkling powdered sugar

noun: a multiple star with 6 components; second brightest in Gemini; close to Pollux