dead horse, to beat/flog a

beat a dead horse

To continue to focus on something—especially an issue or topic—that is no longer of any use or relevance. We've all moved on from that problem, so there's no use beating a dead horse.
See also: beat, dead, horse

flog a dead horse

To continue to focus on something—especially an issue or topic—that is no longer of any use or relevance. We've all moved on from that problem, so there's no use flogging a dead horse.
See also: dead, flog, horse

flog a dead horse

 and beat a dead horse
Fig. to insist on talking about something that no one is interested in, or that has already been thoroughly discussed. The history teacher lectured us every day about the importance of studying history, until we begged him to stop flogging a dead horse. Jill: I think I'll write the company president another letter asking him to prohibit smoking. Jane: There's no use beating a dead horse, Jill; he's already decided to let people smoke.
See also: dead, flog, horse

beat a dead horse

Also, flog a dead horse. Try to revive interest in a hopeless issue. For example, Politicians who favor the old single-tax idea are beating a dead horse. From the 1600s on the term dead horse was used figuratively to mean "something of no current value," specifically an advance in pay or other debt that had to be worked ("flogged") off. [Second half of 1800s]
See also: beat, dead, horse

flog a dead horse

waste energy on a lost cause or unalterable situation.
1971 Cabinet Maker & Retail Furnisher If this is the case, we are flogging a dead horse in still trying to promote the scheme.
See also: dead, flog, horse

ˌflog a dead ˈhorse

(British English, informal) waste your effort by trying to do something that is no longer possible: Pam’s flogging a dead horse trying to organize the theatre trip. It’s quite obvious that nobody’s interested.
If an animal or a person is flogged, it is/they are hit many times with a whip or a stick, usually as a punishment.
See also: dead, flog, horse

dead horse, to beat/flog a

To pursue a futile goal or belabor a point to no end. That this sort of behavior makes no sense was pointed out by the Roman playwright Plautus in 195 b.c. The analogy certainly seems ludicrous; what coachman or driver would actually take a whip to a dead animal? The figurative meaning has been applied for centuries as well; often it is used in politics, concerning an issue that is of little interest to voters. However, some writers, John Ciardi among them, cite a quite different source for the cliché. In the late eighteenth century, British merchant seamen often were paid in advance, at the time they were hired. Many would spend this sum, called a dead horse, before the ship sailed. They then could draw no more pay until they had worked off the amount of the advance, or until “the dead horse was flogged.”
See also: beat, dead, flog