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.

---

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.

---

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

---

castor ² British  

/ ˈkɑːstə /

noun

1. a variant spelling of caster caster

---

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

---

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.

---

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

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 always did think that the very thought of castor oil was enough to make a buzzard sick.

From "Summer of the Monkeys" by Wilson Rawls