What does seaweed mean?
Seaweed is the common name for marine macroalgae, a diverse group of organisms that includes brown, red, and green algae. Unlike ordinary plants, most seaweeds lack true roots, stems, and leaves; they attach to surfaces with structures called holdfasts and absorb nutrients directly from the surrounding water. Seaweed grows on rocky coasts, reefs, and in shallow seas, with giant kelp forming extensive underwater forests. People have long harvested it for food, especially in East Asian cuisines, and it is also used as fertilizer, animal feed, and in products such as alginate and agar. In everyday language, seaweed often suggests flexible strands washed onto beaches, although the term can encompass many very different forms. The word is useful for anyone interested in coastal ecosystems, marine biology, food traditions, or the many surprising industrial applications of algae.
Any of various marine macroalgae, especially brown, red, or green algae growing along coasts and in shallow ocean waters.
"Dense seaweed covered the rocks near the shore."
Often treated as an uncountable collective noun; seaweeds can be used for distinct species or individual organisms.
Marine algae harvested and used as food, fertilizer, animal feed, or industrial material.
"The company sells dried seaweed and seaweed snacks."
This use refers to the harvested material rather than to seaweed as a growing organism.
The countable plural is used for different species or individual organisms; seaweed is also commonly used as an uncountable collective noun.
"The guide described several seaweeds commonly found on the shore."
Under the waves, giant seaweed can form kelp forests that provide food and shelter for an entire underwater community.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does seaweed come from?
The compound seaweed combines sea with weed, both of which are of Germanic origin. The second element comes from Old English wēos, an old term for vegetation or a plant, while sea developed from Old English sæ, originally a body of water. The compound became established in English during the medieval or early modern period and has remained a general word for marine algae.
How seaweed is actually used
Seaweed is generally used as an uncountable collective term for the organisms or material. The countable plural seaweeds is appropriate when referring to different individual species or specimens.
Easily confused with seaweed
Seaweed is a macroalga without true roots, stems, and leaves, whereas seagrass is a flowering vascular plant that grows in shallow marine environments.