From Longman Dictionary of Contemporary Englisharsonistar‧son‧ist /ˈɑːsənɪst $ ˈɑːr-/ noun [countable] someone who commits the crime of arson
Examples from the Corpus
arsonist• A fortnight ago arsonists got inside the building and started a fire.• If it should turn out that the fire was started by an arsonist, the story will take on additional meaning.• This playing both arsonist and fire department is the real cause of the arms race in the region.• Although suspects in many of the other church fires have been arrested and prosecuted, the Salem arsonists remain at large.• Having more combustible straw around only means more fuel for the arsonist.• First he began to shy away from the crowd of young street thug arsonist gunslingers.• Last year arsonists attacked a house in Coventry also earmarked as a clinic. 