Medical Definition of fly
1: a winged insect—usually used in combination <emerging mayflies> <a large butterfly>
2a: any dipteran fly—called also true fly, two-winged flyb: a large and stout-bodied dipteran fly (as a horsefly)
Seen and Heard
What made you want to look up fly? Please tell us where you read or heard it (including the quote, if possible).