(transitive, obsolete) To labour about; labour over; to work hard upon; to ply diligently.
(transitive) To beat or thump (someone) soundly.
1856: Gustave Flaubert, Madame Bovary, Part III Chapter X, translated by Eleanor Marx-Aveling
He saw the village; he was seen coming bending forward upon his horse, belabouring it with great blows, the girths dripping with blood.
(transitive) To attack (someone) verbally.
(transitive) To discuss or explain (something) excessively or repeatedly; to harp on or overelaborate.
1961, John Fitzgerald Kennedy, inaugural speech
Let both sides explore what problems unite us instead of belabouring those problems which divide us.