The Collaborative International Dictionary of English v.0.48:

Biology \Bi*ol"o*gy\, n. [Gr. bi`os life + -logy: cf. F.
   biologie.]
   The science of life; that branch of knowledge which treats of
   living matter as distinct from matter which is not living;
   the study of living tissue. It has to do with the origin,
   structure, development, function, and distribution of animals
   and plants.
   [1913 Webster]

WordNet (r) 3.0 (2006):

biology
    n 1: the science that studies living organisms [syn: biology,
         biological science]
    2: characteristic life processes and phenomena of living
       organisms; "the biology of viruses"
    3: all the plant and animal life of a particular region [syn:
       biota, biology]