noun
1.
a. : a day when troops are given exercises or maneuvers in the field
b. : an outdoor get-together held for entertainment and relaxation
the annual field day of a company union
c. : a day of open-air sports and athletic competition (as in schools)
2. : a thorough general cleaning in the navy
3.
a. : an occasion marked usually by extreme fun or hilarity
the children had a field day when the teacher left the room
b. : an occasion or opportunity for unrestrained ridicule
the newspapers had a field day with the scandal
c. : a period when full opportunity suddenly, unexpectedly, or finally appears to unleash and satisfy natural powers, thwarted ability, or restrained desire
the artillery had a field day with the retreating infantry