The Collaborative International Dictionary of English v.0.48:

Insecticide \In*sec"ti*cide\, n. [Insect + L. caedere to kill.]
   An agent or preparation for destroying insects; an insect
   powder or spray. -- In*sec"ti*ci`dal, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

insecticide
    n 1: a chemical used to kill insects [syn: insecticide,
         insect powder]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "insecticide":
   aborticide, acaricide, anthelmintic, antibiotic, antiseptic,
   bug bomb, carbamate insecticide, chemosterilant,
   chlorinated hydrocarbon insecticide, contact poison, defoliant,
   disinfectant, eradicant, fratricide, fumigant, fungicide, genocide,
   germicide, herbicide, homicide, infanticide, insect powder,
   matricide, microbicide, miticide, organic chlorine,
   organic phosphate insecticide, parricide, patricide, pesticide,
   poison, rat poison, regicide, roach paste, roach powder,
   rodenticide, sororicide, stomach poison, suicide, systemic,
   systemic insecticide, toxic, toxicant, toxin, uxoricide, venin,
   venom, vermicide, virus, weed killer