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

According to a federal complaint, 27-year-old Abdinajib Hassan Yussuf set up a fly-by-night autism center claiming to provide one-on-one therapy for autistic children.

From The Wall Street Journal • Mar. 8, 2026

There are just too many fly-by-night operations that either treat your personal data carelessly or, in some cases, just steal it.

From Seattle Times • Feb. 12, 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