red-letter
[red-let-er]
adjective
marked by red letters, as festival days in the church calendar.
memorable; especially important or happy: a red-letter day in his life.
Origin of red-letter
late Middle English word dating back to 1400–50
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for red-letter
Contemporary Examples of red-letter
Turns out, after all, to be a red-letter day or, that is, a brown-liquid evening.
Historical Examples of red-letter
This may be termed the red-letter year of the Canadian post-office.
The Stamps of CanadaBertram Poole
That will make it another kind of red-letter day—S for S'prise.
The Goody-Naughty BookSarah Cory Rippey
Phœbe's graduation from the Greenwald High School was her red-letter day.
PatchworkAnna Balmer Myers
However that may be, certain it is that this is a red-letter night at the Mermaid.
Shakespeare's Christmas Gift to Queen BessAnna Benneson McMahan
The girl came to count that a red-letter day on which she did not see her mistress.
A Forgotten HeroEmily Sarah Holt