The Collaborative International Dictionary of English v.0.48:

Defecation \Def`e*ca"tion\, n. [L. defaecatio: cf. F.
   d['e]f['e]cation.]
   1. The act of separating from impurities, as lees or dregs;
      purification.
      [1913 Webster]

   2. (Physiol.) The act or process of voiding excrement.
      [1913 Webster]

WordNet (r) 3.0 (2006):

defecation
    n 1: the elimination of fecal waste through the anus [syn:
         defecation, laxation, shitting]