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.

---

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

---

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.”

---

Etymology

Origin of fly-by-night

First recorded in 1790–1800

Example Sentences

That they had been friends for so long before, Ms. Röhm said, made it obvious that their romantic relationship was not a fly by night affair.

From New York Times • Nov. 12, 2021

Nowadays they sleep by day and fly by night.

From New York Times • Dec. 11, 2020

H&R Block probably weeds out most of these but I worry about some of the other "fly by night" tax preparation places. 

From Time • Feb. 9, 2013

Army pigeons are now being taught to fly by night.

From Time Magazine Archive

To this very day the owl has to fly by night.

From Minor Poems Little Classics, Vol. 15 by Johnson, Rossiter