The Collaborative International Dictionary of English v.0.48:

Entelechy \En*tel"e*chy\, n. [L. entelechia, Gr. ?, prob. fr. ?
   ? ? to be complete; ? + ? completion, end + ? to have or
   hold.] (Peripatetic Philos.)
   An actuality; a conception completely actualized, in
   distinction from mere potential existence.
   [1913 Webster]

WordNet (r) 3.0 (2006):

entelechy
    n 1: (Aristotle) the state of something that is fully realized;
         actuality as opposed to potentiality