fly-by-night (flībī-nīt′) Informal
1. Unreliable or unscrupulous, especially with regard to business dealings: "some fly-by-night startup that was halfway to shutting down" (Douglas Edwards).
2. Of an impermanent or insubstantial nature: fly-by-night fashions in clothing.
n. also fly-by-night·er (-nītər)
1. An unreliable or unscrupulous person.
2. One, such as a company, that is short-lived and therefore unreliable.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.