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]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "disinfectant":
   acaricide, anthelmintic, antibiotic, antiseptic, bactericide,
   bleaching powder, bug bomb, carbamate insecticide, carbolic acid,
   chemosterilant, chlorinated hydrocarbon insecticide, chlorine,
   cleaner, cleanser, contact poison, cresol, decontaminator,
   defoliant, eradicant, formaldehyde, fumigant, fumigator, fungicide,
   germicidal, germicide, herbicide, hypochlorous acid, insect powder,
   insecticide, mercuric chloride, microbicide, miticide,
   organic chlorine, organic phosphate insecticide, pesticide, phenol,
   poison, purifier, rat poison, roach paste, roach powder,
   rodenticide, sanitizer, sodium hypochlorite, stomach poison,
   systemic, systemic insecticide, toxic, toxicant, toxin, venin,
   venom, vermicide, virus, weed killer