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• castor
  castor

  noun

  Also a brownish, unctuous substance with a strong, penetrating odor, secreted by certain glands in the groin of the beaver, used in medicine and perfumery.
• Castor
  Castor

  noun

  a star of the second magnitude in the constellation Gemini, the more northerly of the two bright stars in this constellation.

castor

¹ American  

[kas-ter, kah-ster] / ˈkæs tər, ˈkɑ stər /

noun

1. Also a brownish, unctuous substance with a strong, penetrating odor, secreted by certain glands in the groin of the beaver, used in medicine and perfumery.

2. a hat made of beaver or rabbit fur.

3. a heavy woolen cloth used mainly for coats.

4. a beaver.

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Castor ² American  

[kas-ter, kah-ster] / ˈkæs tər, ˈkɑ stər /

noun

Astronomy.

1. a star of the second magnitude in the constellation Gemini, the more northerly of the two bright stars in this constellation.

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Castor ¹ British  

/ ˈkɑːstə /

noun

1. the second brightest star, Alpha Geminorum, in the constellation Gemini: a multiple star consisting of six components lying close to the star Pollux. Distance: 52 light years

2. classical myth See Castor and Pollux

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castor ² British  

/ ˈkɑːstə /

noun

1. a variant spelling of caster caster

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castor ³ British  

/ ˈkɑːstə /

noun

1. the brownish aromatic secretion of the anal glands of a beaver, used in perfumery and medicine

2. the fur of the beaver

3. a hat made of beaver or similar fur

4. a less common name for beaver 1

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Castor Scientific  

/ kăs′tər /

1. A bright multiple star in the constellation Gemini, with a combined apparent magnitude of 0.08. Scientific name: Alpha Geminorum.

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Etymology

Origin of castor¹

1350–1400; Middle English < Latin < Greek kástōr beaver

Origin of Castor²

Named after Castor; see Castor and Pollux

Example Sentences

Castor cited what she described as reckless attacks on other renewable-energy projects—such as wind power—and the independence of the NRC.

From The Wall Street Journal • Jan. 8, 2026

Finally Castor canadensis, long maligned as a pest, is getting a rebrand as an ecological hero.

From Los Angeles Times • Jan. 7, 2025

Tampa Mayor Jane Castor has voiced relief that her city has not seen the type of storm surge that was feared.

From BBC • Oct. 10, 2024

"I’ve said many times that if you want to pick a fight with Mother Nature, she’s winning 100 percent of the time," Tampa Mayor Jane Castor said in a press conference Tuesday.

From Salon • Oct. 9, 2024

He showed up as promised, and delivered his panegyric—but in the course of it, he included a decorative digression, as might have been quite normal practice, in praise of the twin demigods Castor and Pollux.

From "Words Like Loaded Pistols" by Sam Leith