Green’s Dictionary of Slang

to make a toast with a brimming glass.

1784		Hibernian Jrnl 4/2: [H]e was soon knocked up by bumpering His mistress, and bundled home in a hackney coach.
1803		Hants Teleg. 13 June 3/2: [T]the Mayor and Gentlemen were bumpering his Majesty’s health.
1822		Scots Mag. 1 Feb. 8/2: And then their bumpering away, with ‘three-times-three’ — their toasting and bespattering each other with panegyric, even to nauseating loathsomeness.
1835		Bell’s Life in London 10 May 1/3: [S]cenes of gormandizing, bumpering, and drinking of healths.
1841		Worcs. Chron. 10 Nov. 2/4: [H]e felt ,quite certain that they would every one feel a high degree of pleasure bumpering and drinking with honors justly due, the health of Mr. Price.
1842		Dublin Wkly Nation 22 Oct. 9/4: [T]his strange soul has descended to batten on bloody banquet, and drink bumpering treasons with the awful shades of Reynolds.