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

Warmer weather also means there will be a higher chance of blooms of yellow-brown sargassum seaweed washing ashore. —Carley Rojas Avila, Travel + Leisure, 19 July 2025

How about sargassum, the foul-smelling seaweed that washes up on beaches in South Florida and around the world? —Lew Sichelman, Miami Herald, 10 July 2025

Aromas of sweet oak—in contrast to the overly astringent variety—segue into rich herbal and savory meat pie; a tiny thread of seaweed helps boost that umami note, complementing the natural wood sugars well. —David Thomas Tao, Forbes.com, 8 July 2025

At the restaurant, a farm-to-table menu will use ingredients foraged in the area, such as Icelandic herbs, various seaweeds, and berries, as well as products sourced from local ranches, fisheries, and geothermal greenhouses. —AFAR Media, 7 July 2025

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)