Very angry, enraged. The allusion to a hornet, which can launch a fierce attack, captures extreme anger. Variants 'mad as hell,' 'mad as hops,' and 'mad as a wet hen' carry the same meaning.
Examples:
- Mary was mad as a hornet when her purse was stolen.
Origin: 1800s–early 1900s
Synonyms: mad as hell, mad as hops, mad as a wet hen