fast day

a day on which fasting is observed, especially such a day appointed by some ecclesiastical or civil authority.

RELATED WORDS

Middle English word dating back to 1300–50

The fourth of May was appointed a fast-day, and August the twenty-second a day of thanksgiving.
History of the Colony and Ancient Dominion of Virginia|Charles Campbell
When he came to Ayno, he found the Doctor just gone to Church, it being observed by him and his people as a fast-day.
Memorials of the Independent Churches in Northamptonshire|Thomas Coleman
Bad news arrived from America, "about the fleet," and therefore Whitefield kept a fast-day at his houses of worship.
George Whitefield|Joseph Belcher
The “Sunday blood,” the super-superb sartorial equestrian of our annual Fast-day, is not imposing or dangerous.
The Autocrat of the Breakfast-Table|Oliver Wendell Holmes

On the 19th December the King's breakfast was served as usual; but, being a fast-day, he refused to take anything.
Memoirs Of The Court Of Marie Antoinette, Queen Of France, Complete|Madame Campan