A person who deliberately sets fires; an arsonist. Also, a true bug insect that is red and black.
Compound of 'fire' (Old English 'fyr') and 'bug' (origin uncertain, possibly from Welsh 'bwg' meaning ghost or bogey). The term for the insect comes from its fire-like red coloring, while the arsonist sense developed in 19th-century American English.
The same word describes both a colorful insect and a criminal—a perfect example of how English can stretch one word to cover completely different things based on a shared feature (that striking red color). It's like we named the bug first, then metaphorically borrowed the name for someone who creates fire destruction.
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