Douglas Harper's Etymology Dictionary
field-day
1747, originally a day of military exercise and review (see field (v.)); figurative sense "any day of unusual bustle, exertion, or display" [Century Dictionary] is from 1827.\n
Usage examples of "field-day".
CHAPTER LIV Springing a Mine Refreshed by sleep, Mr. Bucket rises betimes in the morning and prepares for a field-day.