castor

1 of 3

noun (1)

cas·​tor ˈka-stər 

1

: beaver sense 1a

2

: castoreum

3

: a beaver hat

castor

2 of 3

cas·​tor

variant spelling of caster

Castor

3 of 3

noun

Cas·​tor ˈka-stər 

1

: one of the Dioscuri

2

: the more northern of the two bright stars in Gemini

Examples of castor in a Sentence

Recent Examples on the Web

Noun

The formula lists a castor-oil derivative, which helps spread the ultra-black, waterproof ink smoothly across the lash line—a plus when lids are drier. —Christa Joanna Lee, Allure, 11 Nov. 2025

Made with hydrolyzed pea protein and castor seed oil, the formula can also enhance overall hair health by strengthening, smoothing, and boosting shine and moisture. —Jenny Berg, Vogue, 11 Nov. 2025

Noun

Packed with skin-loving ingredients like mango butter, green tea extract, and castor seed oil, this cream bronzer keeps your skin hydrated all day long without emphasizing texture or sinking into fine lines. —Allure, 14 Aug. 2025

Meanwhile, castor seed oil, rambutan extract, and a blend of peptides help to nourish your lashes while coating them with high-impact color. —Conçetta Ciarlo, Vogue, 11 Aug. 2025

Word History

Etymology

Noun (1)

Middle English, from Latin, from Greek kastōr, from Kastōr Castor

Noun

Latin, from Greek Kastōr

First Known Use

Noun (1)

14th century, in the meaning defined at sense 1

Noun

15th century, in the meaning defined at sense 1

Phrases Containing castor

• castor bean
• castor oil
• castor-oil plant
• castor sugar

Rhymes for castor

• aster
• blaster
• caster
• faster
• gaster
• laster
• master
• paster
• pastor
• plaster
• raster
• vaster

Kids Definition

Castor

noun

Cas·​tor ˈkas-tər 

: the more northern of the two bright stars in Gemini

Etymology

Noun

from Greek Kastōr (name of one of the twin heroes in mythology) see Word History at gemini