Nightcap
Etymology
A transparent compound of "night" and "cap." It began with the literal woolen cap worn against cold bedrooms, then shifted by analogy to the warming drink that likewise "caps" the day; baseball later borrowed it for the second game of a pair.
noun · /NYT-kap/
A drink taken just before bed — or, literally, a cap once worn to sleep.
What it names
A cozy word for the last drink of the night, with a second life in American sport as the closing game of a doubleheader.
Example
They lingered over one last nightcap before calling it an evening.
Related idea
A nightcap ends the day; a digestif ends the meal — the two often coincide but answer to different rituals.