›the state of burning, or a burning mass of material: [U]The factory had to be closed because the risk of fire was too great.[C]There have been a lot of forest fires because of the drought.[C]The library was badly damaged in the fire.[U]The theater was destroyed by fire.[C]Over a hundred volunteers were needed to put out the fire (= stop it).›A fire is also a small controlled mass of burning material that is used for heating or cooking: [C]Light a fire in the fireplace.on fire›If something is on fire, it is burning, esp. when it is not meant to be: By the time the firefighters arrived, the whole house was on fire.