idioms using “fly”

On the fly

To do something quickly, without planning

“The engineers are building the prototype on the fly, based on their instincts instead of science.”

Fly-over prefecture (or area)

A place considered uninteresting, so one flies over it to a more interesting place

“He is from a fly-over prefecture so no one ever comes to visit him.”

A fly in the ointment

The person or thing that might prevent success or happiness

“Kumiko-san wants to get married in Hawaii but her future in-laws are the fly in the ointment.”

A fly in the wall

To be secretly present at a private meeting

“I’d loved to be a fly on the wall when Keiko-san tells her boss she is leaving the company to start her own business.”

Wouldn’t hurt a fly

A gentle and kind person

“Ogawa-san cannot be responsible for the awful rumors; she wouldn’t hurt a fly.”