How did field day come to mean a time of great success and opportunity? Field would seem to be an odd choice at first blush, but as with many such terms, an examination of its semantic development makes all clear.
Field day originally referred to a day of military exercises. From A Scheme for Equipping and Maintaining Sixteen Men of War, from 1747:
These periodical Intervals of eating and drinking...are to the Citizens as it were Field Days, for improving...their Valour.
By the early 19th century, the term had generalized to mean a day of big events. From an 1827 letter by Thomas Creevey, an English politician:
Saturday was a considerable field day in Arlington Street,...and a very merry jolly dinner and evening we had.
Finally, by the mid-20th century the big events had become great successes. From a letter by Aldous Huxley on 8 December 1969, in which he puns on the “field” in the phrase:
Industrial agriculture is having a field day in the million acres of barren plain now irrigated.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton