seaweedPronunciation: /ˈsiːwiːd/Translate seaweed | into French | into German | into Italian | into Spanish Definition of seaweed noun [mass noun] large algae growing in the sea or on rocks below the high-water mark: seaweed glistened on the rocks [count noun]:seaweeds abound on most shoresseaweed in other Oxford dictionaries Definition of seaweed in the US English dictionary