From the Greek Καστωρ (Kastor) , possibly related to κεκασμαι (kekasmai) "to shine, to excel". In Greek myth Castor was a son of Zeus and the twin brother of Pollux. The constellation Gemini, which represents the two brothers, contains a star by this name. Castor is an old Greek name, whose meaning is "beaver". Castor was the name of one of the characters in Greek mythology, one of the twins who form the star sign of Gemini. This name is not a very popular boy name these days.
