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

Another must-visit is La Martinière, an Île de Ré ice cream institution, which pays homage to local harvests with flavors like potato and oysters with seaweed praline (creamy, briny, and strange, but worth a taste), plus crowd pleasers like caramel with fleur de sel (sea salt). —Caitlin Gunther, Condé Nast Traveler, 19 June 2026

The sandy shores are combed for seaweed and trash nightly, which earned the town a Blue Wave certification. —Tara Massouleh McCay, Southern Living, 17 June 2026

The seaweed choux buns are cloudlike in their lightness. —Jeremy Repanich, Robb Report, 16 June 2026

South Florida beaches have been inundated by waves of sargassum in recent weeks — while visually distasteful to some, the seaweed is not usually harmful to humans, and occupies a critical niche in marine ecosystems. —Sarah Perkel, USA Today, 16 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)