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regular holiday; fixed day off; regular closing day
このお店の定休日は毎週火曜日ですよ。
This shop's regular closing day is Tuesday.
この店の定休日は毎週水曜日です。
This store is closed every Wednesday.
定休日なのに間違えて店に来てしまった。
I mistakenly came to the store on its day off.