Green’s Dictionary of Slang

bitter-gatter n.

beer.

1930		R. Graves Good-bye to All That 94: The Grand Marshal who officiated at my initiation had drunk four or five pints of ‘bitter-gatter’ and a glass or two of ‘juniper’ ( these were secret words ) .
1936		(con. late 19C) F. Richards Old Soldier Sahib [ebook] Those who like their drop of ‘bitter-gatter’ or ‘juniper-brandy’, as beer and gin are called in the secrecy of the Buff lodge.
2023		R. Milward Man-Eating Typewriter 17: Mis Bardo sips a bitter-gator.