The Collaborative International Dictionary of English v.0.48:

Enervation \En`er*va"tion\, n. [L. enervatio: cf. F.
   ['e]nervation.]
   1. The act of weakening, or reducing strength.
      [1913 Webster]

   2. The state of being weakened; effeminacy. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

enervation
    n 1: lack of vitality; "an enervation of mind greater than any
         fatigue"
    2: serious weakening and loss of energy [syn: debilitation,
       enervation, enfeeblement, exhaustion]
    3: surgical removal of a nerve