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

Dishes include king crab cooked in dulce seaweed butter, Perigord black truffle tagliatelle, and citrus cured tuna loin. —Kaitlyn Rosati, New York Daily News, 5 Feb. 2025

In recent decades, seaweed has grown out of control thanks to a die-off of algae-eating animals, such as large sea urchins, and pollution. —Benji Jones, Vox, 4 Feb. 2025

Although seaweed may be widely available, it is often contaminated by heavy metals, contains iodine which is toxic in high amounts, and is a possible carcinogen. —Marianne Krasny, Forbes, 13 Jan. 2025

Shades: 26 Key ingredients: Titanium dioxide (SPF), seaweed extract, sesame seed oil, alfalfa seed powder, sweet almond seed meal, eucalyptus leaf oil Size: 1 oz. —Kiana Murden, Vogue, 10 Jan. 2025

Word History

First Known Use

1577, in the meaning defined at sense 1a

Kids Definition

seaweed

noun

sea·​weed -ˌwēd 

: a plant growing in the sea

especially : a marine alga (as a kelp)