cyanobiont UK /ˌsaɪ.ə.nəʊˈbaɪ.ɒnt/US /ˌsaɪ.ə.noʊˈbaɪ.ɑnt/ noun1 •A cyanobacterium that lives in symbiosis a eukaryote; a cyanobacterial photobiont. formscyanobionts