Entry 1 sense Webster, 1913 Nemathelminthes · Nem·a·thel·min·thes · IPA 01 prop. n. pl. An order of helminths, including the Nematoidea and Gordiacea; the roundworms. 1. An order of helminths, including the Nematoidea and Gordiacea; the roundworms.(Zool.)