The Collaborative International Dictionary of English v.0.48:

Ninepins \Nine"pins\, n. pl.
   A game played with nine pins, or pieces of wood, set on end,
   at which a wooden ball is bowled to knock them down; bowling.
   [1913 Webster]

   Note: In the United States, ten pins are used for this game,
         which is therefore often called tenpins.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tenpins \Ten"pins\, n.
   A game resembling ninepins, but played with ten pins. See
   Ninepins. [U. S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

tenpins
    n 1: bowling down an alley at a target of ten wooden pins [syn:
         tenpins, tenpin bowling]