CastorPronunciation: /ˈkɑːstə/Definition of Castor 1 Greek Mythology the twin brother of Pollux. See Dioscuri. 2 Astronomy the second-brightest star in the constellation Gemini, close to Pollux. It is a multiple star system, the three components visible in a moderate telescope being close binaries. Castor in other Oxford dictionaries Definition of Castor in the US English dictionary
