Source : Webster's Revised Unabridged Dictionary (1913)

Sulk \Sulk\, n. [L. sulcus.]
   A furrow. [Obs.]

Sulk \Sulk\, v. i. [See {Sulkiness}.]
   To be silently sullen; to be morose or obstinate. --T. Hook.

Source : WordNet®

sulk
     n : a mood or display of sullen aloofness or withdrawal; "stayed
         home in a sulk" [syn: {sulkiness}]
     v : be in a huff and display one's displeasure; "She is pouting
         because she didn't get what she wanted" [syn: {pout}, {brood}]