The Collaborative International Dictionary of English v.0.48:

brooder \brood"er\ n.
   a box designed to maintain a constant temperature by the use
   of a thermostat; used for chicks or premature infants.

   Syn: incubator.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

brooder
    n 1: apparatus consisting of a box designed to maintain a
         constant temperature by the use of a thermostat; used for
         chicks or premature infants [syn: incubator, brooder]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "brooder":
   Bantam, banty, barn-door fowl, barnyard fowl, biddy, birthplace,
   breeding place, broiler, broody hen, capon, chanticleer, chick,
   chickabiddy, chicken, chicken house, chicky, cock, cockerel, coop,
   cradle, depressive, domestic fowl, drake, duck, duckling,
   dunghill fowl, forcing bed, fowl, fryer, game fowl, gander,
   gloomy Gus, gobbler, goose, gosling, guinea cock, guinea fowl,
   guinea hen, hatchery, hen, hen turkey, hencote, henhouse, hennery,
   hotbed, incubator, melancholiac, melancholic, mope, nest, nidus,
   nursery, partlet, poulard, poult, poultry, pullet, roaster,
   rookery, rooster, setting hen, sourpuss, spring chicken,
   stewing chicken, tom, tom turkey, turkey, turkey gobbler,
   turkey-cock