"castor" in the noun sense
1. Castor, Alpha Geminorum
a multiple star with 6 components second brightest in Gemini close to Pollux
2. caster, castor
a shaker with a perforated top for sprinkling powdered sugar
3. caster, castor
a pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable
4. beaver, castor
a hat made with the fur of a beaver (or similar material)
5. Castor, genus Castor
type genus of the Castoridae: beavers
Source: WordNet® (An amazing lexical database of English)
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