[flahy-bahy-nahyt] /ˈflaɪ baɪˌnaɪt/

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-nighter
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.
unreliable or untrustworthy, esp in finance
brief; impermanent
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

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.

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.”


Undependable and dishonest: fly-bynight correspondence school


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  • Fly-by-wire

    [flahy-bahy-wahyuh r] /ˈflaɪ baɪˈwaɪər/ adjective 1. (of aircraft or spacecraft) activated entirely by electronic controls. noun 1. aircraft control through systems operated by electronic circuits rather than mechanical rods FBW noun, adjective a semiautomated computerized flight control for flying aircraft or spacecraft

  • Fly-block

    noun, Machinery, Nautical. 1. (in a Spanish burton or the like) a block, supported by a runner, through which the hauling part of the fall is rove. 2. any block that shifts with the movement of its tackle.

  • Fly-book

    noun, Angling. 1. a booklike case for artificial flies.

  • Fly-boy

    [flahy-boi] /ˈflaɪˌbɔɪ/ noun 1. Printing. 1 (def 29b). 2. Slang. noun An aircraft pilot, esp an intrepid one in the US Air Force: The generals are no full-throttle ”fly-boys” (WWII armed forces)

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