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]