red-letter day(redirected from Red letter day)
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A very important or significant day. My college graduation was a real red-letter day for my whole family.
Fig. an important or significant day. (From the practice of printing holidays in red on the calendar.) Today was a red-letter day in our history. It was a red-letter day for our club.
A special occasion, as in When Jack comes home from his tour of duty, that'll be a red-letter day. This term alludes to the practice of marking feast days and other holy days in red on church calendars, dating from the 1400s. [c. 1700]
n. an important day that might well be marked in red on the calendar. Today was a red-letter day in our history.