Source : Webster's Revised Unabridged Dictionary (1913)

Depletion \De*ple"tion\, n. [Cf. F. d['e]pl['e]tion.]
   1. The act of depleting or emptying.

   2. (Med.) the act or process of diminishing the quantity of
      fluid in the vessels by bloodletting or otherwise; also
      excessive evacuation, as in severe diarrhea.

Source : WordNet®

depletion
     n 1: the act of decreasing something markedly
     2: the state of being depleted