The Collaborative International Dictionary of English v.0.48:

Actualisation \Ac`tu*al*i*sa"tion\, Actualization
\Ac`tu*al*i*za"tion\, n.
   A making actual or really existent; giving the appearance of
   reality. [R.] --Emerson.

   Syn: realization, realisation.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

actualisation
    n 1: making real or giving the appearance of reality [syn:
         realization, realisation, actualization,
         actualisation]