day of days

plural days of days

1. idiomaticA particularly noteworthy day; the day on which a milestone or especially memorable event occurs.

   At last came the day of days, my release.

   1907, Jack London, The Pen: Long Days in a County Penitentiary

   3 more examples

   "It is a day of days," she said, as I approached; "a day of all days either to live or die. . . . I am dying, yet shall I live."

   1850, Edgar Allan Poe, Morella

   It was a day of days for California railbirds. Not only was it the day of the $100,000 Santa Anita Handicap, world's richest horse race, but this was the now-or-never race for doughty old Seabiscuit, darling of U. S. racing fans, Cinderella of the turf.

   1940 March 11, “Sport: Four Hundred Grand”, in Time, retrieved 09 Jul 2015

   Super Saturday has been the centerpiece of the United States Open for nearly three decades. But this day of days is heading toward a multimillion-dollar extreme makeover.

   2012 September 8, George Vecsey, “Tennis: Rain and Rest Days Spell the End of Super Saturday”, in New York Times, retrieved 09 Jul 2015

   Synonyms: red-letter day

2. capitalizedsometimesChristianitySunday, especially Easter Sunday.

   To be sure, Christians celebrate the Resurrection of Christ every Sunday, but there is a special place for the celebration we call Easter. It should be approached as the Day of Days.

   2009, Charles G. Fuller, Give Him Time, →ISBN, page 107

   1 more example

   The residents skirting the line of the Harlem Railroad as far as Croton Falls, were not a little annoyed, last Sunday, by numerous cheap excursion trains. . . . [W]e doubt whether the law gave being to a great corporation for the purpose of tempting men from their homes on the Day of days.

   1863 June 7, “To the Editor: Sunday Railway Excursions”, in New York Times, retrieved 09 Jul 2015

1. alternativeuncountableAlternative form of day of days.