red-letter

[ red-let-er ]
/ ˈrɛdˈlɛt ər /

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

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