An insecticide is a chemical used to kill insects. Farmers spray it on crops. People put it around the house for cockroaches or mosquitoes. It can be a spray, a powder, a bait, or even a special soap — the point is to kill the insect, not just to push it away. Though actually, many people say insecticide and pesticide as if they were one word. Pesticide is the bigger family: it can be for insects, weeds, fungi, or rats. An insecticide is only for insects. It is a practical word, a little formal in English, but anyone who gardens or farms knows it. Handle it as a real chemical: useful, and not for children to touch.