Dictionary

beat a dead horse en · VERB

(idiomatic) To persist or continue far beyond any purpose, interest or reason.
- I won’t stop beating this dead horse until (male) TV executives stop this sexist practice. 2016, Anthony Livingston Hall, The iPINIONS Journal: Commentaries on the Global Events of 2015, volume XI, iUniverse, →ISBN:
- After having shown us three hours of instructional and safety videos, the inspector was simply beating a dead horse by telling us to buckle up as we got into the van.
- A friend, the political scientist Irving Bernstein, told me that political scientists and historians are inclined to regard the question of objectivity as a dead horse that one should stop beating, and maintained that it is not the scholar but the lay person who has problems with objectivity. 1999, Fredrick Carl Redlich, Hitler: Diagnosis of a Destructive Prophet, Oxford University Press, →ISBN, page xii:
- The library director believes the argument about “professionalism” is a “dead horse we should stop beating.” 1992, William A. Katz, Reference Services and Reference Processes, McGraw-Hill, →ISBN, page 220:

Spelling	Features	Labels	Source
flog a dead horse		alternative	lexicographic
beating a dead horse	Tense=Pres, VerbForm=Part		lexicographic
beats a dead horse	Number=Sing, Person=3, Tense=Pres		lexicographic
beat a dead horse	Tense=Past, VerbForm=Part	colloquial	lexicographic
beat a dead horse	Tense=Past		lexicographic
beaten a dead horse	Tense=Past, VerbForm=Part		lexicographic