nemertean Syllabification: (ne·mer·te·an)Pronunciation: /niˈmərtēən/ (also nemertine /ˈnemərˌtēn/) ZoologyDefinition of nemertean noun a member of the small phylum Nemertea; a ribbon worm. adjective relating to or denoting nemerteans. nemertean in other Oxford dictionaries Definition of nemertean in the British & World English dictionary