The Collaborative International Dictionary of English v.0.48:

Preparatory \Pre*par"a*to*ry\, a. [L. praeparatorius: cf. F.
   pr['e]paratoire.]
   Preparing the way for anything by previous measures of
   adaptation; antecedent and adapted to what follows;
   introductory; preparative; as, a preparatory school; a
   preparatory condition.
   [1913 Webster]

WordNet (r) 3.0 (2006):

preparatory
    adj 1: preceding and preparing for something; "preparatory
           steps" [syn: preparatory, preparative,
           propaedeutic]