preposition

preposition (http://definr.com/preposition)

     n 1: a function word that combines with a noun or pronoun or noun
          phrase to form a prepositional phrase that can have an
          adverbial or adjectival relation to some other word
     2: (linguistics) the placing of one linguistic element before
        another (as placing a modifier before the word it modifies
        in a sentence or placing an affix before the base to which
        it is attached)