IPA: /ˈnaɪt.kæp/
KK: /ˈnaɪtˌkæp/
A drink, often alcoholic, that is consumed just before going to bed.
After a long day, he enjoyed a nightcap to help him relax before sleep.
Nightcap → The word is formed from "night" (from Old English "niht", meaning the period of darkness) and "cap" (from Old French "cape", meaning a covering or head covering). A nightcap originally referred to a cap worn at night, and it has evolved to mean a drink taken before bed, metaphorically covering one for the night.
Think of the 'darkness' of 'night' and a 'covering' like a 'cap' — a nightcap is something that covers you as you sleep, like a drink before bed.
No commonly confused words.