black letter day

== English == === Alternative forms === black-letter day === Noun === black letter day (plural black letter days) A day marked in ancient calendars in black letter, as distinguished from the more import red letter days; an inauspicious day. Coordinate term: red letter day === Further reading === William Dwight Whitney, Benjamin E[li] Smith, editors (1911), “black-letter day”, in The Century Dictionary […], New York, N.Y.: The Century Co., →OCLC.