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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

• castors
  plural

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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Other Word Forms

Noun Inflected Forms

• castors
  plural

Etymology

Origin of castor¹

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

Origin of Castor²

Named after Castor; see Castor and Pollux

Example Sentences

See Examples For:

castor Castor castors

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

From BBC ● Mar. 31, 2026

The modified Arabidopsis overcame metabolic bottlenecks and produced significant amounts of an oil similar to castor oil that it doesn't naturally produce.

From Science Daily ● Apr. 30, 2024

Look for products that contain petroleum jelly, castor oil and glycerin, Rogers said.

From Seattle Times ● Feb. 5, 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

I thought, “Oh, no! If she gives me a dose of castor oil, and then starts reading to me, I will surely die.”

From "Summer of the Monkeys" by Wilson Rawls

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

Tampa Mayor Jane Castor called the incident "devastating" in a statement on X.

From BBC ● Nov. 8, 2025

The highest ever Powerball jackpots were both won in California — in Nov. 2022 when Edwin Castor of Altadena purchased a ticket worth $2.04 billion and in Oct.

From Los Angeles Times ● Aug. 25, 2025

"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

Everyone’s dripping in sweat—especially Castor and Pollux in their insect shells—and Cressida calls for a break.

From "Mockingjay" by Suzanne Collins

As for the metallic pepperpot-shaped aliens, created by designer Raymond Cusick, Ms Webb remembers rehearsals with actors "trolleying" around on castors in just the bottom halves of the characters that would become The Doctor's nemesis.

From BBC ● Dec. 21, 2023

Honours ended up even, though the smooth-striding Everett glided round as if on castors, while the solidly carved sprint specialist noticeably sagged in his final strides.

From The Guardian ● May 29, 2020

It's odd at first; Stewart seems dazed by the noisiness of the production, to be moving as if on castors.

From Los Angeles Times ● Nov. 4, 2016

The sculptural giltwood pedestal includes leopard masks above three paw feet that conceal recessed brass castors.

From Architectural Digest ● Jan. 14, 2015

He was then the warmest boy anywhere about; and fully appreciated the cheering influence of "the castors"—he did not go upon castors for a long time afterward, and never again to the same extent.

From Graham's Magazine Vol XXXII No. 1 January 1848 by Robert Taylor Conrad