Green’s Dictionary of Slang

1. a drink [it ‘goes down’].

1674		T. Duffet Epilogue Spoken by Heccate and Three Witches 33: Here’s six go-downs of humming Stygian Liquor.
1690		D’Urfey Collin’s Walk canto 4: And many more whose quality Forbids their toping openly, Will privately, on good occasion, Take six go-downs on Reputation.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 64: Their crazy Noddles were a little warm’d by [...] large Dropsical Go-downs of mild and stale.
1719		T. Killigrew Chit-Chat III ii: Three Go-downs of you would do me more good than warm water.
1891		F.W. Carew Autobiog. of a Gipsey 435: I fortified myself with two stiff go-downs of brandy and water.

2. (US black) a basement flat or apartment (cf. go-up n.).

1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1989		M. Amis London Fields 445: Keith’s keys, his gaoler’s keys, keys for Debbee, Trish and Analiese, keys for flat, for car, for go-down and lock-up.