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.

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.
See also: letter, red
Farlex Partner Idioms Dictionary
See also:
  • a red-letter day
  • all day long
  • day by day
  • just another day at the office
  • from day to day
  • make a day of (doing something)
  • make a day of doing
  • make a day of it
  • any day now
  • any minute, day, time, etc. now