This
database is a comprehensive collection of all the American idioms and slang available.
American Idioms are many and varied. We hope you enjoy our collection. We are adding more all the time.
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(UK) If someone is trying to convince people to do or feel something without any hope of succeeding, they're flogging a dead horse.
This is used when someone is trying to raise interest in an issue that no-one supports anymore; beating a dead horse will not make it do any more work.