Source : Webster's Revised Unabridged Dictionary (1913)

Deerstalker \Deer"stalk`er\, n.
   One who practices deerstalking.

Deerstalker \Deer"stalk`er\, n.
   A close-fitting hat, with a low crown, such as is worn in
   deerstalking; also, any stiff, round hat. [Eng.]

Source : WordNet®

deerstalker
     n : a tight-fitting hat with visors front and back; formerly
         worn by hunters