- have a great time doing something enjoyable
- a day of excitement
- an opportunity to do something you enjoy doing
- a great deal to do, especially at someone else's expense
- The children had a field day when they were taken on a trip to the museum.
- Our boss did not turn up today, so we had a field day at office. None of us did any work.
- The media had a field day when the news of the minister's illicit affair was leaked.
- The team building trip was a great success. We had a field day playing games, singing, dancing and enjoying ourselves.
- The press had a field day when rumours broke out that the celebrity couple were getting separated.
- With no one to supervise them, the kids had a field day, running all over the house, breaking things and generally creating a huge mess.
The phrase originates from the military. It was used in the literal sense, for a day spent in the field, doing manoeuvers and drills, and the first reference is found in 1747, in Scheme Equip. Men of War. Over the years, it began to be used with reference to other events as well, and by the 20th century, the current meaning was well in use.