- Castor, Alpha Geminorum - a multiple star with 6 components; second brightest in Gemini; close to Pollux
--1 is a kind of multiple star
--1 is a member of Gemini - caster, castor - a shaker with a perforated top for sprinkling powdered sugar
--2 is a kind of shaker
- caster, castor - a pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable
--3 is a kind of roller
- beaver, castor - a hat made of beaver fur or similar material
--4 is a kind of fur hat
- Castor, genus Castor - type genus of the Castoridae: beavers
--5 is a kind of mammal genus
--5 is a member of Castoridae, family Castoridae
--5 has members: beaver