heliozoan Syllabification: (he·li·o·zo·an)Pronunciation: /ˌhēlēəˈzōən/ ZoologyDefinition of heliozoan noun a single-celled aquatic animal of the phylum Heliozoa. adjective relating to or denoting heliozoans. heliozoan in other Oxford dictionaries Definition of heliozoan in the British & World English dictionary