The Collaborative International Dictionary of English v.0.48:

Biologist \Bi*ol"o*gist\, n.
   A student of biology; one versed in the science of biology.
   [1913 Webster]

WordNet (r) 3.0 (2006):

biologist
    n 1: (biology) a scientist who studies living organisms [syn:
         biologist, life scientist]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "biologist":
   anatomist, animal physiologist, anthropologist, bacteriologist,
   biochemist, biometrist, biophysicist, botanist, conchologist,
   cytologist, ecologist, entomologist, ethologist, geneticist,
   helminthologist, herpetologist, ichthyologist, malacologist,
   mammalogist, natural scientist, naturalist, ophiologist,
   ornithologist, physiologist, protozoologist, taxidermist,
   zoo-ecologist, zoographer, zoologist, zoonomist, zoopathologist,
   zoophysicist, zootaxonomist