- an antipollution device in an automotive exhaust system that contains a catalyst for chemically converting some pollutants in the exhaust gases, as carbon monoxide, unburned hydrocarbons, and oxides of nitrogen, into harmless compounds.
- a device using three-way catalysts to reduce the obnoxious and poisonous components of the products of combustion (mainly oxides of nitrogen, carbon monoxide, and unburnt hydrocarbons) from the exhausts of motor vehicles
