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; Castor and Pollux

Example Sentences

Ricin, a highly toxic chemical, is a poison found naturally in castor beans.

From BBC • Mar. 31, 2026

Those oils could replace the reliance of growing dangerous crops, like castor.

From Science Daily • Apr. 30, 2024

Newer products include a hair strengthening collection with biotin and Jamaican castor oil, and a wig care collection that uses apple cider vinegar to remove build-up from weaves and wigs.

From Los Angeles Times • Nov. 2, 2023

The viscous mixture of castor oil and medicine is painful going in and leaves lumps in its wake.

From Seattle Times • Feb. 8, 2023

To insure my speedy recovery, Grandma came after me with castor oil.

From "Warriors Don't Cry: A Searing Memoir of the Battle to Integrate Little Rock's Central High" by Melba Pattillo Beals