say it: KA-stur
castor is a noun meaning "a multiple star with 6 components; second brightest in Gemini; close to Pollux". It carries 5 recorded senses.
a multiple star with 6 components; second brightest in Gemini; close to Pollux
a shaker with a perforated top for sprinkling powdered sugar
type genus of the Castoridae: beavers
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for castor come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.