Webster's Revised Unabridged Dictionary · 1913

Castor

Castor , noun

[Latin castor the beaver, Greek {not transcribed}; of uncertain origin.]

1.
(Zoology) A genus of rodents, including the beaver. See Beaver.
2.
Castoreum. See Castoreum.
3.
A hat, esp. one made of beaver fur; a beaver.
I have always been known for the jaunty manner in which I wear my castor. — Sir W. Scott
4.
A heavy quality of broadcloth for overcoats.

Castor , noun

See Caster, a small wheel.

Castor , noun

[Latin]

(Astronomy) the northernmost of the two bright stars in the constellation Gemini, the other being Pollux.

Castor , noun

[The minerals castor and pollux were so named because found together on the island of Elba. See Castor and Pollux.]

(Mineralogy) A variety of the mineral called petalite, from Elba.

Also: Castorite