Green’s Dictionary of Slang

1. very wet weather; a very wet day.

1864		Derby Day 40: ‘Wet day.’ ‘Reg’lar soaker, mate,’ replied Ted.
1866		J. Greenwood Little Ragamuffin 254: If it ain’t set in for an all-night soaker its werry strange to me.
1904		Western Times (Wales) 19 Aug. 13/5: Perhaps the soaker we had then gave them a sickener of the country, and no wonder.
1908		D.G. Phillips Susan Lenox II 119: Ain’t this rain a soaker?
1914		H. Chapin letter 1 Dec. in Soldier and Dramatist (1916) 42: Yesterday again was a soaker.
1949		‘Josephine Tey’ Brat Farrar 205: ‘It’s going to be perfect weathe [...] I can remember only one real soaker at Bures’.

2. (US tramp) an unpleasant, sickening experience.

1899		J. Flynt Tramping with Tramps 388: ‘Oh, it was a soaker [a sickening experience], Cig’ he said.
1927		in ‘Jargon of the Und.’ in DN V.