Source : Webster's Revised Unabridged Dictionary (1913)

Grimness \Grim"ness\, n. [AS. grimnes.]
   Fierceness of look; sternness; crabbedness; forbiddingness.

Source : WordNet®

grimness
     n 1: the quality of being ghastly [syn: {ghastliness}, {gruesomeness},
           {luridness}]
     2: something hard to endure; "the asperity of northern winters"
        [syn: {asperity}, {hardship}, {rigor}, {rigour}, {severity},
         {rigorousness}]