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

Fat-blocking microbeads made with green tea, vitamin E and seaweed could offer a new way to lose weight and a potential alternative to popular GLP-1 drugs and bariatric surgery, according to exploratory new research. —Deirdre Bardolf, FOXNews.com, 3 Sep. 2025

Body treatments and massages incorporate natural ingredients, such as local honey, Ayurvedic plant extracts, and seaweed oils. —Patricia Doherty, Travel + Leisure, 2 Sep. 2025

This article will highlight 3 sectors that seaweed is making waves. —Dianne Plummer, Forbes.com, 1 Sep. 2025

Researchers coated the beads with alginate, a type of seaweed fiber, to protect them from the acidic environment of the stomach. —Jay Kakade august 30, New Atlas, 30 Aug. 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)