fly-by-night

American  

[flahy-bahy-nahyt] / ˈflaɪ baɪˌnaɪt /

adjective

1. not reliable or responsible, especially in business; untrustworthy.

   a fly-by-night operation.

2. not lasting; brief; impermanent; transitory.

   a fly-by-night theater.

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noun

1. a person or thing that is unreliable, especially a debtor who evades or attempts to evade creditors.

2. a person regarded as a poor credit risk.

fly-by-night British  

adjective

1. unreliable or untrustworthy, esp in finance

2. brief; impermanent

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noun

1. an untrustworthy person, esp one who departs secretly or by night to avoid paying debts

2. a person who goes out at night to places of entertainment

fly-by-night Cultural  

1. Shady or untrustworthy: “Before buying stock in a newly formed company, the prudent investor will check its owners' credentials to make sure it's not a fly-by-night operation.”

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Etymology

Origin of fly-by-night

First recorded in 1790–1800

Example Sentences

The proliferation of fly-by-night flags and registers has fanned concern about possible accidents involving old tankers with sanctioned cargoes, but until the recent seizures Western governments have mostly allowed them to sail unimpeded.

From The Wall Street Journal • Jan. 11, 2026

Some are on fly-by-night commercial websites that reveal little information about who runs them or the technology they’re based on.

From Seattle Times • May 23, 2024

Experts say the problem is fueled by the ease of setting up a fly-by-night operation online to move goods.

From Washington Times • Jan. 1, 2024

But she doesn’t consider Chaudhari’s team to be like other fly-by-night investors.

From Los Angeles Times • May 25, 2023

Those jars were something you might expect to find in the basement of a fly-by-night medical school, not a house full of children.

From "Miss Peregrine's Home for Peculiar Children" by Ransom Riggs