pesticide - any chemical substance intended to kill or control pests. Common pesticides are: insecticides, rodenticides, herbicides, fungicides, and bactericides. Petroleum products and their petrochemical derivatives are important in the formulation of many types of pesticides. Specialized petroleum oils are used to kill insects by suffocation (see orchard spray oil); other petroleum products serve as solvents or diluents for the active component. See agricultural oil.