Source : Webster's Revised Unabridged Dictionary (1913)

Lassitude \Las"si*tude\, n. [L. lassitudo, fr. lassus faint,
   weary; akin to E. late: cf. F. lassitude. See {Late}.]
   A condition of the body, or mind, when its voluntary
   functions are performed with difficulty, and only by a strong
   exertion of the will; languor; debility; weariness.

         The corporeal instruments of action being strained to a
         high pitch . . . will soon feel a lassitude. --Barrow.

Source : WordNet®

lassitude
     n 1: a state of comatose torpor (as found in sleeping sickness)
          [syn: {lethargy}, {sluggishness}]
     2: a feeling of lack of interest or energy [syn: {languor}, {listlessness}]
     3: weakness characterized by a lack of vitality or energy [syn:
         {inanition}, {lethargy}]