WordNet (r) 3.0 (2006):

first base
    n 1: the base that must be touched first by a base runner in
         baseball
    2: the fielding position of the player on a baseball team who is
       stationed at first of the bases in the infield (counting
       counterclockwise from home plate) [syn: first base,
       first]
    3: the initial stage in accomplishing something; "we didn't get
       to first base with that approach"