Sometimes you need a reason to celebrate, and sometimes you don't. Today we pay tribute to celebrations both on and off the calendar with a look at the term red-letter day.

The expression red-letter day first appeared in print in the early 1700s, but the practice of printing letters in red on calendars is far, far older. For hundreds of years, ecclesiastical calendars used red letters to indicate holy days (which of course, were also holidays); by the 1400s, red-letter had become shorthand for "a red letter that indicates a holy day on a calendar." Over time, red-letter left the Church and developed the secular senses of "special significance; happy; or memorable."

Red-letter days are the opposite of quotidian days. Quotidian has its roots in a Latin word meaning "each day; daily," and in its 700+ years in English, its senses haven't strayed very far at all from its origin. Initially, quotidian meant occurring "every day"; it then developed the sense "belonging to each day; or everyday"; and eventually it came to mean "commonplace or ordinary."

The old Roman equivalent to "red-letter" was the white stone. The Romans used the method of piling up stones of black and white a sort of diary. The black stones marked bad days, the whites good ones. Lewis Carroll wrote of days he "marked with a white stone" in his diaries.

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