WordNet (r) 3.0 (2006):

tic-tac-toe
    n 1: a game in which two players alternately put crosses and
         circles in one of the compartments of a square grid of nine
         spaces; the object is to get a row of three crosses or
         three circles before the opponent does [syn: ticktacktoe,
         ticktacktoo, tick-tack-toe, tic-tac-toe, tit-tat-
         toe, noughts and crosses]