"entire dictionary" day
A wearily-humorous term to describe a long strenuous exhausting day that literally begins and ends with the very first and very last words in the dictionary, respectively --- you frenetically "hit the ground running" with a wailing whoop of haste and/or alarm ("Aaaaaaaaaaahhhh!!!") at the crack of dawn, and then never stop your "headlong dash" till you collapse into bed that night ("Zzzzzzzzzzzz").
Last weekend I volunteered to host the entire youth-camp group on assorted activities and outings --- it was definitely an "entire dictionary" day which I would not be physically or emotionally capable of repeating very often, but the youngsters were all smiling and happily-grateful to me afterwards, and so that made it all worth it.