Green’s Dictionary of Slang

a bracing drink, a ‘pick-me-up’.

1881		Western Times 20 Sept. 3/4: The multiform nomenclature under which refreshments seem to be presented. A ‘livener,’ a ‘cooler,’ a ‘nerver’.
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’.
1891		Sporting Times 21 Feb. 3/2: Swizzle retired to take a nerver.
1902		H. Baumann Londinismen (2nd edn).