helianthus Syllabification: (he·li·an·thus)Pronunciation: /ˌhēlēˈanTHəs/Definition of helianthus noun a plant of the genus Helianthus in the daisy family, especially (in gardening) a sunflower. Origin:modern Latin, from Greek hēlios 'sun' + anthos 'flower'helianthus in other Oxford dictionaries Definition of helianthus in the British & World English dictionary