hair·​worm ˈher-ˌwərm How to pronounce hairworm (audio)
: any of a phylum (Nematomorpha) of elongated worms that have separate sexes, are parasitic in arthropods as larvae, and are free-living in water as adults

called also horsehair worm

: any of a genus (Capillaria) of nematode worms that include serious parasites of the digestive tract of fowls and tissue and organ parasites of mammals

Example Sentences

Recent Examples on the Web Swimming with the fishesSpinochordodes tellinii, also known as a hairworm, are free-living aquatic organisms as adults, who, as nematodes, eek out an existence in the mud. Christie Wilcox, Discover Magazine, 31 Oct. 2015 Paragordius obamai, a hairworm that lives inside the stomachs of African crickets. Lisa M. Krieger, The Mercury News, 9 Jan. 2017 For his part, Obama also has a trapdoor spider, a species of lichen, a puffbird, a parasitic hairworm that infects crickets, and an extinct lizard called Obamadon named after him. Richard Pyle, National Geographic, 2 Sep. 2016

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'hairworm.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History

First Known Use

1658, in the meaning defined at sense 1

Time Traveler
The first known use of hairworm was in 1658

Dictionary Entries Near hairworm

Cite this Entry

“Hairworm.” Dictionary, Merriam-Webster, Accessed 22 Mar. 2023.

Kids Definition


hair·​worm ˈha(ə)r-ˌwərm How to pronounce hairworm (audio)
: any of various very long slender worms (as a horsehair worm)

Medical Definition


: any nematode worm of the genus Capillaria

More from Merriam-Webster on hairworm

Love words? Need even more definitions?

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

Which Came First?

  • baby chick with a brown egg
  • hot take or cold shoulder?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Solve today's spelling word game by finding as many words as you can with using just 7 letters. Longer words score more points.

Can you make 12 words with 7 letters?