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

The Sea to Soul treatment, for example, uses soothing Pacific seaweed fronds, warm kelp water, and a green tea seaweed salt glow exfoliation to target muscle tension and a glacial clay mask to firm the skin. — Condé Nast, Condé Nast Traveler, 6 Oct. 2026

Look for notes of black pepper, vanilla, citrus, and maple over an assertive, smoky base made up of flavors like iodine, seaweed, campfire, and licorice, and just a touch of heat on the finish at 46 percent ABV. — Jonah Flicker, Robb Report, 5 Oct. 2026

Set on a remote island off the Chilean coast, the film stars Manuela Oyarzún as Silvia, a woman who makes a living harvesting seaweed and leads an isolated existence with her partner. — Elsa Keslassy, Variety, 5 Oct. 2026

In Indonesia, Birufinery is building a higher-value market for the country’s abundant seaweed by developing biostimulant products for agriculture. — Denni Hu, Footwear News, 24 Sep. 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)