From A Little Cloud in James Joyce’s Dubliners:
“And to clinch the bargain,” said Little Chandler, “we’ll just have one more now.”
Ignatius Gallaher took out a large gold watch and looked at it.
“Is it to be the last?” he said. “Because you know, I have an a.p.”
“O, yes, positively,” said Little Chandler.
“Very well, then,” said Ignatius Gallaher, “let us have another one as a deoc an doruis—that’s good vernacular for a small whisky, I believe.”
Don Gifford’s Joyce Annotated gives this as – “Irish: (literally) a door-drink; one for the road.” The Scottish version is Deoch an doris (drink of the door).
There’s also a French variant which I’ve never encountered except in books – le coup de l’étrier – literally ‘drink/glass of the stirrup.’ Huysmans uses it in ch. 11 of À Rebours: “Voyons, fit-il, pour se verser du courage, buvons le coup de l’étrier; et il remplit un verre de brandy, tout en réclamant sa note.”
The Italian version – which I’ve heard used but as something closer to English nightcap – is an exact equivalent of the French – Bicchiere della staffa