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]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "biology":
   aerobiology, agrobiology, anatomy, animal physiology, anthropology,
   astrobiology, bacteriology, biochemics, biochemistry, biochemy,
   bioecology, biological science, biometrics, biometry, bionics,
   bionomics, biophysics, botany, cell physiology,
   comparative anatomy, conchology, cryobiology, cybernetics,
   cytology, ecology, electrobiology, embryology, entomology,
   enzymology, ethnobiology, ethology, exobiology, genetics,
   gnotobiotics, helminthology, herpetology, ichthyology,
   life science, malacology, mammalogy, microbiology,
   molecular biology, ornithology, pharmacology, physiology,
   protozoology, radiobiology, taxidermy, taxonomy, virology,
   xenobiology, zoogeography, zoography, zoology, zoonomy,
   zoopathology, zoophysics, zootaxy, zootomy