We found 16 dictionaries that define the word fly on the wall:

General (10 matching dictionaries)

1. fly-on-the-wall: Merriam-Webster
2. fly on the wall, fly on the wall: Oxford Learner's Dictionaries
3. fly on the wall: Collins English Dictionary
4. fly-on-the-wall, fly on the wall: Cambridge Advanced Learner's Dictionary
5. fly on the wall: Wiktionary
6. Fly on the Wall (Bobby V album), Fly on the Wall (song), Fly on the Wall (video), Fly-on-the-wall, Fly on the wall (disambiguation), Fly on the wall, The Fly on the Wall: Wikipedia, the Free Encyclopedia
7. Fly-on-the-wall: TheFreeDictionary.com
8. Fly on the wall: Phrase Finder
9. fly on the wall: Longman Dictionary of Contemporary English

Business (1 matching dictionary)

10. Fly-on-the-wall: Legal dictionary

Computing (1 matching dictionary)

11. Fly-on-the-wall: Encyclopedia

Medicine (1 matching dictionary)

12. Fly-on-the-wall: Medical dictionary

Miscellaneous (2 matching dictionaries)

13. AbbreviationZ (No longer online)
14. Fly-on-the-wall: Idioms

Slang (1 matching dictionary)

15. fly-on-the-wall, fly on the wall: Urban Dictionary

Definitions from Wiktionary (fly on the wall) ▸ noun:  (idiomatic) A quiet, non-participating, or unseen observer; an eavesdropper or witness. Similar: eavesdropper, onlooker, watcher, looker-on, on-looker, observer, bystander, looker, viewer, spotter, more... Opposite: participant, involved, engaged, active, present ▸ Words similar to fly on the wall ▸ Usage examples for fly on the wall ▸ Idioms related to fly on the wall ▸ Wikipedia articles (New!) ▸ Words that often appear near fly on the wall ▸ Rhymes of fly on the wall ▸ Invented words related to fly on the wall