fly-in I. \ˈ ̷ ̷ˌ ̷ ̷\noun Etymology: from fly in, v. 1.: an act of flying to a destination < planned the fly-in of the rescue planes > 2.: an outdoor theater planned for the patronage of persons remaining in their private planes — compare drive-in II. noun : a gathering (as at a small airport) of flying enthusiasts who arrive by private plane