a red letter day
red-letter day
A very important or significant day. My college graduation was a real red-letter day for my whole family.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a red letter day
a pleasantly memorable, fortunate, or happy day.In Church calendars, a saint's day or church festival was traditionally distinguished by being written in red letters.
Farlex Partner Idioms Dictionary © Farlex 2017