1. 1. Any of numerous two-winged insects of the order Diptera, especially any of the family Muscidae, which includes the housefly.
   2. Any of various other flying insects, such as the caddis fly.
2. A fishing lure simulating a fly, made by attaching materials such as feathers, tinsel, and colored thread to a fishhook.

fly in the ointment

1. A detrimental circumstance or detail; a drawback.

[Middle English flie, from Old English flēoge.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.