Green’s Dictionary of Slang

1. a drink used as a ‘pick-me-up’, usu. the first drink of the day.

1865		Chambers Jrnl 11 Feb. 82/1: As on the Sunday morning these persons were sure to wake up with ‘the horrors’ — an affliction known only to the full by those who have got drunk upon beer-shop beer — so they were as sure to want a ‘livener’ and most of them used to make their weay to the Prince of Orange.
1867		Islington Gaz. 17 Dec. 2/6: On Wedbnesday night he came home intoxicated, and in the morning asked [...] for a ‘livener’ (a cup of tea with some gin in it).
1881		Western Times 20 Sept. 3/4: The multiform nomenclature under which refreshments seem to be presented. A ‘livener,’ a ‘cooler,’ a ‘nerver’.
1883		J. Greenwood Tag, Rag & Co. 138: He was that low-spirited about Jack that he didn’t feel like sitting down to coffee, and he should go to the Pied Bull and have a ‘livener’.
1888		Sheffield Eve. Teleg. 14 July 2/2: In a book [...] ‘American and Other Drinks’ we find [...] the ‘Flash of Lightning,’ the ‘Nerver,’ the ‘Livener,’ and the ‘Locomotive’.
1895		Chelmsford Chron. 24 May 5/7: he obtained the bottle of beer, which he wanted for a ‘livener,’ [...] from a man named Porter.
c.1900		Harrington & LeBrunn [perf. Marie Lloyd] The Coster’s Christening 🎵 The men went out for ‘liveners’ an’ a little drop for us!
1906		Gloucester Citizen 29 Sept. 5/5: he wanted a ‘livener’ before starting to ‘get his nervesd up’. He had at least five two-penny-worths of whiskey.
1910		‘Doss Chiderdoss’ ‘The Blokes Outside’ Sporting Times 6 Aug. 1/4: He mixed another ‘livener’.
1914		E. Pugh Cockney At Home 163: Every mornin’ at eleven he used to slip out o’ the office [...] an’ ’ave his livener in the private bar.
1923		Exeter & Plymouth Gaz. 11 Sept. 8/5: The greatest punishment of all for a man like me who has had a terrible lot of drink, is having to get over it without a ‘livener’ in the cell the next morning.
1928		Western Dly Press 20 Sept. 7/6: In the old days they wanted a ‘livener’ ay five in the morning.
1938		L. Ortzen Down Donkey Row 53: Just going dahn the frog and toad to have a livener.
2001		K. Sampson Outlaws (ms.) 117: Right back in the barrio having a quiet drink. A little livener in your own local with people that you know and trust.

2. a small portion of a drug, used for a similar purpose, although the time of day is irrelevant.

2000		J.J. Connolly Layer Cake 20: I’m only having a fuckin livener.
2015		I. Welsh Decent Ride 73: Jonty, ah’m jist huvin a wee bit ay a livener.