The Collaborative International Dictionary of English v.0.48:

Vivisection \Viv`i*sec"tion\, n. [L. vivus alive + E. section:
   cf. F. vivisection. See Vivid, and Section.]
   The dissection of an animal while alive, for the purpose of
   making physiological investigations.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vivisection
    n 1: the act of operating on living animals (especially in
         scientific research)