Definition of "fast-day" [fast-day]

• A day on which fasting is observed; specifically, a day appointed for fasting as a religious observance by some recognized authority, ecclesiastical or civil; in the most restricted ecclesiastical sense, a day on which, or on part of which, total abstinence from food is prescribed, in contradistinction to a day on which a limitation is imposed on the kind or quantity of food to be taken, called a day of abstinence. See fast, n. (noun)
• In Scotland, a day set apart for humiliation and prayer; specifically, a day thus observed during the week immediately preceding certain celebrations of the Lord's supper. (noun)

The Century Dictionary (Public Domain)

• "Another time, when my aunt again asked for fast-day food they answered: "Why, citoyenne, don't you know what has taken place? none but fools believe all that.""
• "He intimated hopes of future reward, and of instant reimbursement for loss of time, and even of character, by travelling on the state business on the fast-day."
• "For us, senor, every day is fast-day — only without the fish."