from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A day set aside for sports or athletic competition.
- n. An outdoor meeting, social event, or festivity.
- n. A day for military exercises, maneuvers, or display.
- n. Informal A time of great pleasure, activity, or opportunity: The media had a field day with the sensational story.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A parade day.
- n. A school day for athletic events; a sports day.
- n. A day of class taken away from school for a field trip.
- n. A great time or a great deal to do.
- n. A great time or a great deal to do, at somebody else's expense.
- n. Top-to-bottom all-hands cleaning.
from the GNU version of the Collaborative International Dictionary of English
- n. A day of unusual exertion or display; a gala day.
from The Century Dictionary and Cyclopedia
- n. A day when troops are drawn up for instruction in field exercises and evolutions.
- n. Hence Any day of unusual bustle, exertion, or display.
- n. A day when explorations, scientific investigations, etc., as of a society, are carried on in the field.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a day for outdoor athletic competition
- n. a day devoted to an outdoor social gathering
- n. a time of unusual pleasure and success
- n. (military) a day for military exercises and display
Apparently the idiom is derived from the military use. A parade is much easier than the soldiers’ usual drilling and forced exercise. (Wiktionary)