The Collaborative International Dictionary of English v.0.48:

firefighter \fire"fight`er\, fire fighter \fire"
fight`er\(f[imac]r"f[imac]`t[~e]r), n.
   A person whose occupation it is to go to the scene of an
   unwanted fire and extinguish it; a member of a fire company;
   a fireman[1] or a woman who fights fires.

   Note: Some towns have few or no professional firefighters,
         and fire suppression is conducted mostly by groups of
         volunteers, called volunteer firefighters. The term
         fireman[1] was at one time synonymous with firefighter,
         until women began to engage in the same occupation.
         [PJC]

WordNet (r) 3.0 (2006):

fire fighter
    n 1: a member of a fire department who tries to extinguish fires
         [syn: fireman, firefighter, fire fighter, fire-
         eater]