Green’s Dictionary of Slang

a drink; when quenching one’s thirst; esp. as modest quencher.

1841		Dickens Old Curiosity Shop (1999) 270: Mr Swiveller replied that he had very recently been assuaging the pangs of thirst, but that he was still open to ‘a modest quencher.’.
1857		T. Hughes Tom Brown’s School-Days (1896) 11: We must really take a modest quencher, for the down air is provocative of thirst.
1877		H. Hartigan Stray Leaves (1st ser.) 275: We joined in a solemn ‘quencher’.
1881		Bulletin (Sydney) 5 Feb. 13/1: Bringing it back, he handed it to the footman, who first of all took a regular quencher; then Lord Redesdale […] quietly remarked : ‘Oh, by the by, when your master comes in, tell him that the Earl of Redesdale called to see him.’.
1895		‘’Arry on the Elections’ in Punch 27 July 39/1: I lapped off a quart in one quencher.
1895		C. Crowe Aus. Sl. Dict. 49: Modest Quencher, a glass of spirits and water.
1895		Mirror of Life 4 May 10/3: [L]ong enough to imbibe a modest quencher.
1900		Punch 14 Mar. 188/2: After the best news from the Transvaal, the thirst for details was so great as not to be more than partially allayed by ‘cocktails’ or any other ‘modest quencher,’ to quote Mr. Richard Swiveller.
1901		H. Nisbet Hermes 62: Come below and have a quencher [F&H].