1
plural seaweeds
: any of various aquatic and chiefly marine brown, red, or green algae (such as rockweed, gulfweed, and kelp) that often grow in masses, typically have leaflike blades (see blade entry 1 sense 2e), are usually anchored to a solid substrate (such as a rock) by holdfasts (see holdfast sense 2a), and include some (such as dulse, laver, and sea lettuce) that are used as food
… many seaweeds have floats called pneumatocysts, filled with oxygen or carbon dioxide.—Michael Le Page
The word seaweed is broad and refers generally to marine macroalgae, which are algae living in salt or brackish water and visible to the eye.—Elyse Inamine
2
: a mass or growth of seaweeds
… soft crabs were easily visible in the seaweed, because the water was crystal clear then.—Keith Walters
3
: harvested seaweed or seaweed parts used especially as food, fertilizer, and in cosmetics
… sushi rolls wrapped in thin sheets of dried seaweed …—Jane Snow
Cite this Entry
“Seaweed.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/seaweed. Accessed 15 Jul. 2026.
Copy CitationLove words? Need even more definitions?
Merriam-Webster unabridged
