Definitions of Castor:

noun: type genus of the Castoridae: beavers
noun: a multiple star with 6 components; second brightest in Gemini; close to Pollux
noun: a hat made of beaver fur 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
name: A surname (rare: 1 in 50000 families; popularity rank in the U.S.: #5833)