The Collaborative International Dictionary of English v.0.48:

2-hitter \2-hitter\ n.
   1. a game in which a pitcher allows the opposing team only 2
      hits.

   Syn: two-hitter
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

2-hitter
    n 1: a game in which a pitcher allows the opposing team only 2
         hits [syn: two-hitter, 2-hitter]