noun
day off drinking; liver rest day
Jocular term for a day when one abstains from alcohol to give the liver a rest. A pun on 休館日 (day a facility is closed).
今日は休肝日だから、お酒は飲まない。
Today is a liver rest day, so I won't drink alcohol.
週に二日は休肝日を設けている。
I set aside two days a week as alcohol-free days.