flatworm

noun

flat·​worm ˈflat-ˌwərm 

: any of a phylum (Platyhelminthes) of soft-bodied usually much flattened acoelomate worms (such as the planarians, flukes, and tapeworms)

called also platyhelminth

Examples of flatworm in a Sentence

Recent Examples on the Web

April showers may bring May flowers, but in Texas, heavy rains have brought something else entirely: Invasive hammerhead flatworms. —Melissa Locker, Southern Living, 16 June 2025

The new species belongs to a group of flatworms known as planarians, which are typically non-parasitic. —Irene Wright, Miami Herald, 9 Apr. 2025

According to the Texas Invasive Species Institute, the flatworms can be killed with orange essence and salt and sprayed with vinegar or a combination of vinegar and citrus oil. —Danielle Jennings, Peoplemag, 24 July 2024

Two species of the flatworms were discovered in California’s freshwater fish, according to a study published Tuesday in the Journal of Infectious Diseases. —Karen Garcia, Los Angeles Times, 4 June 2025

Word History

First Known Use

1874, in the meaning defined above

Kids Definition

flatworm

noun

flat·​worm -ˌwərm 

: 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

flatworm

noun

flat·​worm ˈflat-ˌwərm 

: any worm of the phylum Platyhelminthes : platyhelminth

especially : turbellarian