red letter day

An allusion to the practice, dating to classical antiquity, of marking important days in red on calendars.

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

• day of days
• red letter date