red letter day

plural red letter days · alternative red-letter day

1. A day marked in red on calendars; a church feast day.

   The only red-letter day occurring in July, is the twenty-fifth, called St James's Day.

   1825, Christian Gleaner and Domestic Magazine, Volume 2, page 161

   1 more example

   But the monsters who interrupt men in the middle of a sentence are to be found everywhere; and they are always practising. Red-letter days or black-letter days, festival or fast, makes no difference to them.

   1893, Thomas De Quincey, “Conversation and Coleridge”, in Alexander H. Japp, editor, The Posthumous Works of Thomas De Quincey, volume II, London: William Heinemann

2. idiomaticA particularly significant day; a day of personal or sectarian celebration.

   Monday was a red letter day for her. She accomplished a lot and had fun doing it.

   4 more examples

   We saw losses for days in a row, but Black Tuesday was the worst red letter day of them all.

   "In the meantime, the St. Valentine's Day Massacre at Chicago was a red-letter day in the gangster wars."

   1975, John Ankenbruck, Twentieth Century History of Fort Wayne, page 286

   So I assume that we all have some red letter days that are precious to our memories—maybe a first date, a wedding, a gift, a word of encouragement, a vacation, a graduation or a trip to an interesting place. I had one of those red letter days when I was a young boy, perhaps five or six years old.

   2007, Clyde Wilton, Wilton's Wit, iUniverse, page 3

   2010, Eric Braun, Doris Day, Hachette, Revised and updated edition, unnumbered page, That was, indeed, a red-letter day in my filmgoing life, and a red-letter day in my literary life was when I was asked to write a new biography of Doris Day.

   Synonyms: day of days, red letter date