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

Choi, the founder of Geem seaweed snacks, said seeing her products in mainstream grocery stores means coming full circle for her experience as an Asian American. —Laya Neelakandan, CNBC, 29 May 2026

Much of the company’s work happens in London, far from the seaweed farms that supply its core ingredient. —Justin Worland, Time, 28 May 2026

Her recent 'Sisters of the Sea' project documents the lives and labor of female seaweed farmers in a coastal town in South India. —Rana Wehbe Watson, Forbes.com, 27 May 2026

Seaweed and Closures Limit Beach Options Beachgoers across the region are encountering large amounts of sargassum seaweed washing ashore. —Abby Dodge, CBS News, 23 May 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)