seagrassPronunciation: /ˈsiːɡrɑːs/Definition of seagrass noun [mass noun] a grass-like plant that lives in or close to the sea, especially eelgrass. Genera Cymodocea (family Cymodoceaceae), Zostera (family Zosteraceae), and others seagrass in other Oxford dictionaries Definition of seagrass in the US English dictionary