Source : Webster's Revised Unabridged Dictionary (1913)

Prepositional \Prep`o*si"tion*al\, a. [Cf. F.
   pr['e]positionnel.]
   Of or pertaining to a preposition; of the nature of a
   preposition. --Early. -- {Prep`o*si"tion*al*ly}, adv.

Source : WordNet®

prepositional
     adj : of or relating to or formed with a preposition;
           "prepositional phrase"