Source : Webster's Revised Unabridged Dictionary (1913)

Castor \Cas"tor\, n. [L. castor the beaver, Gr. ?; of uncertain
   origin.]
   1. (Zo["o]l.) 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 \Cast"or\, n.
   See {Caster}, a small wheel.

Castor \Cas"tor\, n. [L.] (Astron.)
   the northernmost of the two bright stars in the constellation
   Gemini, the other being Pollux.

Castor \Cas"tor\, Castorite \Cas"tor*ite\, n. [The minerals
   castor and pollux were so named because found together on the
   island of Elba. See {Castor and Pollux}.] (Min.)
   A variety of the mineral called petalite, from Elba.

Source : WordNet®

Castor
     n 1: a multiple star with 6 components; second brightest in
          Gemini; close to Pollux [syn: {Alpha Geminorum}]
     2: a shaker with a perforated top for sprinkling powdered sugar
        [syn: {caster}]
     3: a pivoting roller attached to the bottom of furniture or
        trucks or portable machines to make them movable [syn: {caster}]
     4: a hat made of beaver fur or similar material [syn: {beaver}]
     5: type genus of the Castoridae: beavers [syn: {genus Castor}]