ON THE FLY

{adv. phr.} 1. While in the air; in flight. * /The bird caught a bug on the fly./ * /Joe was called out because the catcher caught the ball on the fly./ 2. {informal} Between other activities; while busy with many things. * /The president was so busy that he had to dictate letters on the fly./ * /John is very busy, and people who want to talk to him have to catch him on the fly./ Compare: ON THE GO, ON THE WING(2).