not reliable or responsible, especially in business; untrustworthy: a fly-by-night operation.
not lasting; brief; impermanent; transitory: a fly-by-night theater.

noun Also fly-by-night·er.

a person or thing that is unreliable, especially a debtor who evades or attempts to evade creditors.
a person regarded as a poor credit risk.

Origin of fly-by-night

First recorded in 1790–1800 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for fly-by-night

Contemporary Examples of fly-by-night

  • Some of the groups have been around for decades, others are fly-by-night.

    The Daily Beast logo
    Welcome to Assadville, USA

    Christopher Moraff

    November 11, 2014

  • And not fly-by-night issues either, but stalwarts such as G.E., Citi, Google.

    The Daily Beast logo
    Return of the Day Trader

    Lee Eisenberg

    April 9, 2009

Historical Examples of fly-by-night

  • She certainly has acted like a fly-by-night up to this time.

  • He'll be out with a fly-by-night troupe afore the next month.

  • Shown up in our newspapers as a ditch-digger—a fly-by-night—a nobody!

    The Landloper

    Holman Day

  • Had the wind been directly astern, the course of the Fly-by-Night would have been smoother.

    Janice Day

    Helen Beecher Long

  • Torched on by that fly-by-night who'll be getting out of town and who'll be forgotten inside a week.

British Dictionary definitions for fly-by-night



unreliable or untrustworthy, esp in finance
brief; impermanent

noun Also: fly-by-nighter

an untrustworthy person, esp one who departs secretly or by night to avoid paying debts
a person who goes out at night to places of entertainment
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for fly-by-night

1796, slang, said to be an old term of reproach to a woman signifying that she was a witch; extended 1823 to "anyone who departs hastily from a recent activity," especially while owing money. The two senses involve the two verbs fly.

Online Etymology Dictionary, © 2010 Douglas Harper

fly-by-night in Culture


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.”

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.