The Collaborative International Dictionary of English v.0.48:

Entomology \En`to*mol"o*gy\, n.; pl. Entomologies. [Gr.
   'e`ntomon insect (so called because nearly cut in two, fr.
   'e`ntomos cut in; 'en in + te`mnein to cut) + -logy: cf. F.
   entomologie. See In, and Tome, and cf. Insect.]
   1. That part of zo["o]logy which treats of insects.
      [1913 Webster]

   2. A treatise on the science of entomology.
      [1913 Webster]

WordNet (r) 3.0 (2006):

entomology
    n 1: the branch of zoology that studies insects [syn:
         entomology, bugology]