Source : Webster's Revised Unabridged Dictionary (1913)

Glumness \Glum"ness\, n.
   Moodiness; sullenness.

Source : WordNet®

glumness
     n 1: an atmosphere of depression and melancholy; "gloom pervaded
          the office" [syn: {gloom}, {gloominess}]
     2: a gloomy ill-tempered feeling [syn: {moroseness}, {sullenness}]