The Collaborative International Dictionary of English v.0.48:

Prerequisite \Pre*req"ui*site\, a.
   Previously required; necessary as a preliminary to any
   proposed effect or end; as, prerequisite conditions of
   success.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prerequisite \Pre*req"ui*site\, n.
   Something previously required, or necessary to an end or
   effect proposed.
   [1913 Webster]

         The necessary prerequisites of freedom.  -- Goldsmith.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prerequisite
    adj 1: required as a prior condition or course of study
    n 1: something that is required in advance; "Latin was a
         prerequisite for admission" [syn: prerequisite,
         requirement]