- any worm of the phylum Platyhelminthes, having bilateral symmetry and a soft, solid, usually flattened body, including the planarians, tapeworms, and trematodes; platyhelminth.
- any parasitic or free-living invertebrate of the phylum Platyhelminthes, including planarians, flukes, and tapeworms, having a flattened body with no circulatory system and only one opening to the intestine
