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.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.