seaweed

noun

sea·​weed ˈsē-ˌwēd 

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

Examples of seaweed in a Sentence

Recent Examples on the Web

Residents who have discussed the issue online described the smell as one of the most unpleasant aspects of the ongoing seaweed buildup. —Kelly McGreal, FOXNews.com, 13 June 2026

The beaches of South Florida are currently clogged with bristly, stinky and downright annoying piles of seaweed known as sargassum. —Bill Kearney, Sun Sentinel, 12 June 2026

Some of the seaweed is scooped up and sent to a park where it is allowed to decompose and become rich soil, saving the city $100,000 a year in dumping fees. —Joan Murray, CBS News, 10 June 2026

The nooks and crannies of the standing coral skeletons provide an opportunity for the seaweeds, which compete with coral for reef space, to proliferate and take over the reef, preventing the return of corals. —John Kominoski, The Conversation, 10 June 2026

Word History

First Known Use

1577, in the meaning defined at sense 1a

Rhymes for seaweed

• accede
• agreed
• airspeed
• alkyd
• bindweed
• chickweed
• concede
• decreed
• duckweed
• exceed
• flaxseed
• impede

Kids Definition

seaweed

noun

sea·​weed -ˌwēd 

: a plant growing in the sea

especially : a marine alga (as a kelp)