black-letter day

It is only some weeks after the black-letter day, the Great Parnitha Mountain was partially destroyed that this incident came to light.

Days of Optional Observance ("black-letter days")

Moreover, throughout the year the particular day of the week on which Innocents' Day had fallen the previous year was also regarded as a black-letter day, and was also called Innocents' Day.

Popular superstitions concerning lucky and unlucky days, the existence of which has already been referred to in connection with the Romans, were reinforced in the Middle Ages by the recognition of black-letter days in the ecclesiastical calendar.

There are commemorations on this date in the church calendars of members of the Anglican Communion, initially as one of the "days of optional devotion" in the American Book of Common Prayer (1979), and a "black-letter day" in the Church of England's Alternative Service Book.