plural noun

: a family of large mayflies that include forms having shining transparent wings as adults and as nymphs very large mandibles curved out at the tips, feathered gills extending over the body, and enlarged front legs adapted for digging in stream and lake bottoms

Word History


New Latin, from Ephemera, type genus + -idae

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!

Dictionary Entries Near Ephemeridae

Cite this Entry

“Ephemeridae.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/Ephemeridae. Accessed 17 Apr. 2024.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!