A more thorough explanation:

Definition: An arsonist is a person who intentionally sets fire to property or buildings.

Example: The police arrested the arsonist who had set fire to the abandoned warehouse.

Explanation: The example illustrates the definition of an arsonist as someone who deliberately starts a fire. In this case, the arsonist set fire to an empty building, which could have caused harm to people nearby or damaged other properties. Arson is a serious crime that can result in severe consequences, including imprisonment and fines.