Source : Webster's Revised Unabridged Dictionary (1913)

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

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

         The necessary prerequisites of freedom.  -- Goldsmith.

Source : WordNet®

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