The Collaborative International Dictionary of English v.0.48:

Exhaustion \Ex*haus"tion\, n. [Cf. F. exhaustion.]
   1. The act of draining out or draining off; the act of
      emptying completely of the contents.
      [1913 Webster]

   2. The state of being exhausted or emptied; the state of
      being deprived of strength or spirits.
      [1913 Webster]

   3. (Math.) An ancient geometrical method in which an
      exhaustive process was employed. It was nearly equivalent
      to the modern method of limits.
      [1913 Webster]

   Note: The method of exhaustions was applied to great variety
         of propositions, pertaining to rectifications and
         quadratures, now investigated by the calculus.
         [1913 Webster]

WordNet (r) 3.0 (2006):

exhaustion
    n 1: extreme fatigue
    2: serious weakening and loss of energy [syn: debilitation,
       enervation, enfeeblement, exhaustion]
    3: the act of exhausting something entirely