flat·​worm ˈflat-ˌwərm How to pronounce flatworm (audio)
: any of a phylum (Platyhelminthes) of soft-bodied usually much flattened acoelomate worms (such as the planarians, flukes, and tapeworms)

called also platyhelminth

Example Sentences

Recent Examples on the Web Euhaplorchis californiensis, for one, is a trematode flatworm that, in its larval stage, looks a bit like a sperm, with a big head and long tail. Rachel Nuwer, Scientific American, 28 Apr. 2022 Killifish typically spend their days hiding, however, which runs counter to the flatworm’s agenda. Rachel Nuwer, Scientific American, 28 Apr. 2022 Researchers say the blue-green flatworm may have come from Mozambique. The Washington Post, Arkansas Online, 7 Feb. 2022 An investigation by the USGS at the time confirmed the presence of a parasitic flatworm in the swans from Wolf Lake. Carrie Napoleon, chicagotribune.com, 28 Dec. 2021 Many of the immune system’s players are transient molecules, and unearthing evidence of them now may prove nearly impossible — like trying to find a fossil of a jellyfish or a flatworm. Megan Molteni, BostonGlobe.com, 15 Nov. 2021 While wormwood has been researched5 for its possible antiparasitic effects in animals, a recent study6 looking at its efficacy in treating a type of flatworm infection in humans was later retracted. Casey Gueren, SELF, 19 Aug. 2021 In the sixty years since Samuel first published his seminal machine learning work, artificial intelligence has advanced from being not as smart as a flatworm to having less common sense than a house cat. Gil Press, Forbes, 28 May 2021 Some of the most important discoveries of his career hinge on the planarian—a type of flatworm about two centimetres long that, under a microscope, resembles a cartoon of a cross-eyed phallus. Matthew Hutson, The New Yorker, 3 May 2021 See More

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

Word History

First Known Use

1874, in the meaning defined above

Time Traveler
The first known use of flatworm was in 1874

Dictionary Entries Near flatworm

Cite this Entry

“Flatworm.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/flatworm. Accessed 6 Dec. 2022.

Kids Definition



flat·​worm -ˌwərm How to pronounce flatworm (audio)
: any of a phylum of simple worms (as planarians, flukes, or tapeworms) that have a soft flat body, lack a body cavity, and have bilateral symmetry

Medical Definition



flat·​worm ˈflat-ˌwərm How to pronounce flatworm (audio)
: any worm of the phylum Platyhelminthes : platyhelminth
especially : turbellarian

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