a chemical used to kill pests (as rodents or insects)
"The farmer sprayed pesticide on the crops to eliminate the infestation of field mice and beetles."
Anything, especially a synthetic substance but also any substance (e.g. sulfur), or virus, bacterium, or other organism, which kills or suppresses the activities of pests.
"The farmer applied a natural predator to his crops as an alternative pesticide that would suppress aphid populations without using harsh chemicals."
In plain English: A pesticide is any chemical used to kill insects, weeds, fungi, or other pests that damage plants and crops.
"The farmer sprayed pesticide on his crops to protect them from insects."
Usage: Pesticide is an umbrella term that includes herbicides for weeds and insecticides for bugs, not just one specific type of chemical. It refers to both synthetic products like DDT and natural substances such as sulfur used to kill pests in agriculture or gardening.
The word pesticide combines the English words pest and -cide, meaning killer, to describe a substance used to kill harmful insects or animals. It entered modern usage by directly merging these two concepts into a single term for agricultural chemicals.