castoryoudaoicibaDictYouDict[castor 词源字典]
castor: There are two distinct words castor in English. The older originally meant ‘beaver’ [14], and was early used with reference to a bitter pungent substance secreted by glands near the beaver’s anus, employed in medicine and perfumery. The term castor oil [18] probably comes from the use of this oil, derived from the seed of a tropical plant, as a substitute for castor in medicine.

The more recent castor [17] is simply a derivative of the verb cast; it was originally (and still often is) spelled caster. Its use for sprinkling or ‘throwing’ sugar is obvious (the term castor sugar dates back to the mid 19th century), but its application to a ‘small swivelling wheel’ is less immediately clear: it comes from a now obsolete sense of the verb, mainly nautical, ‘veer, turn’: ‘Prepare for casting to port’, George Nares, Seamanship 1882.
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castor (n.)youdaoicibaDictYouDict
late 14c., "beaver," from Old French castor (13c.), from Latin castor "beaver," from Greek Kastor, literally "he who excels," name of one of the divine twins (with Pollux), worshipped by women in ancient Greece as a healer and preserver from disease.

His name was given to secretions of the animal (Latin castoreum), used medicinally in ancient times. (Through this association his name replaced the native Latin word for "beaver," which was fiber.) In English, castor is attested in this sense from c. 1600. Modern castor oil is first recorded 1746; it is made from seeds of the plant Ricinus communis but supposedly possesses laxative qualities (and taste) similar to those of beaver juice, and thus so named.