eelgrass Syllabification: (eel·grass)Pronunciation: /ˈēlˌgras/Definition of eelgrass noun 1a marine plant with long ribbonlike leaves that grows in coastal waters and brackish inlets. Zostera marina, family Zosteraceae 2North Americananother term for tape grass.eelgrass in other Oxford dictionaries Definition of eelgrass in the British & World English dictionary