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

Herbaceous hints of seaweed and vegetal peat add a dry, herbal, smoky edge. —Joseph V Micallef, Forbes, 20 Mar. 2025

Key Ingredients: Apple extract, hyaluronic acid, red seaweed extract Shades: 15 Finish: Natural Size: 1.6 oz. —Jenny Berg, Vogue, 14 Mar. 2025

Other innovation projects in the works include making use of the seaweed that collects on beaches and costs the county millions to remove and improve the passenger experiences at the airport. —Ashley Miznazi, Miami Herald, 12 Mar. 2025

Most types of seaweed are rich in vitamin C, iodine, and zinc.2 Studies have shown these nutrients help keep the immune system working effectively.7 Studies also show that the compounds carrageenans from seaweed offer many immune-boosting effects. —Chelsea Rae Bourgeois, Rdn, Ld, Health, 10 Mar. 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)