noun
two-day hangover; hangover that lasts into the third day
Colloquial term for a hangover that persists two days after drinking, i.e., on the third day. Often used humorously or to emphasize a severe hangover. Compare with 二日酔い (a regular next-day hangover).
See also: 二日酔い
昨日は飲みすぎて、今日は三日酔いだ。
I drank too much yesterday, and now I have a two-day hangover.
三日酔いでまだ頭が痛い。
I still have a headache from this lingering hangover.
二日酔い is the common term for a hangover the day after drinking. 三日酔い specifically refers to a hangover that continues into the second day after drinking (i.e., the third day).
Compound of 三日 (みっか, 'third day of the month; three days') and 酔い (よい, 'drunkenness; hangover'). The term is a playful extension of 二日酔い (ふつかよい, 'hangover'), implying the hangover lasts an extra day.