fly by

WordReference Random House Learner's Dictionary of American English © 2025

fly•by or fly-by /ˈflaɪˌbaɪ/   n. [countable] , pl. -bys. 

1. Aeronautics, Aerospace the flight of a spacecraft past a heavenly body.

WordReference Random House Unabridged Dictionary of American English © 2025

fly•by  (flī′bī′), n., pl. -bys. 

1. Aeronautics, Aerospace the flight of a spacecraft close enough to a celestial object, as a planet, to gather scientific data.
2. Aeronautics
   • Also called flypast. a low-altitude flight of an aircraft for the benefit of ground observers.
   • flyover (def. 1).

Also, fly′-by′. 

• noun, nominal use of verb, verbal phrase fly by 1950–55, American.