Source : Webster's Revised Unabridged Dictionary (1913)

Evacuation \E*vac`u*a"tion\, n. [L. evacuatio: cf. F.
   ['e]vacuation.]
   1. The act of emptying, clearing of the contents, or
      discharging. Specifically:
      (a) (Mil.) Withdrawal of troops from a town, fortress,
          etc.
      (b) (Med.) Voidance of any matter by the natural passages
          of the body or by an artificial opening; defecation;
          also, a diminution of the fluids of an animal body by
          cathartics, venesection, or other means.

   2. That which is evacuated or discharged; especially, a
      discharge by stool or other natural means. --Quincy.

   3. Abolition; nullification. [Obs.] --Hooker.

   {Evacuation day}, the anniversary of the day on which the
      British army evacuated the city of New York, November 25,
      1783.

Source : WordNet®

evacuation
     n 1: the act of removing the contents of something [syn: {emptying},
           {voidance}]
     2: the act of evacuating; leaving a place in an orderly
        fashion; especially for protection
     3: the bodily process of discharging waste matter [syn: {elimination},
         {excretion}, {excreting}, {voiding}]