- The definition of a dayfly is a thin insect that lives in freshwater for about a year and lives as an adult on land for a few hours to a few days.
An example of a dayfly is a mayfly.
The adult mayfly or dayfly.
dayfly definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
noun pl. dayflies
the adult mayfly
dayfly definition by American Heritage Dictionary