The Collaborative International Dictionary of English v.0.48:

disinfectant \dis`in*fect"ant\, n.
   That which disinfects, especially an agent for killing or
   removing the microorganisms which cause infection. Commonly
   used disinfectants are chlorine, sodium hypochlorite
   solution, hydrogen peroxide, and alcohol.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

disinfectant
    adj 1: preventing infection by inhibiting the growth or action
           of microorganisms [syn: bactericidal, disinfectant,
           germicidal]
    n 1: an agent (as heat or radiation or a chemical) that destroys
         microorganisms that might carry disease [syn:
         disinfectant, germicide, antimicrobic,
         antimicrobial]