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

While some seaweed is edible, sargassum seaweed found in Florida is generally not recommended to eat due to potential health risks. —Ashley Miznazi, Miami Herald, 9 May 2025

My favorites included the creamy soup duo of avocado and corn served with flowers of the season and the marinated northern oysters with seaweed, a spicy, citrusy acevichada sauce, and yellow pepper. —Liz Humphreys, Travel + Leisure, 1 May 2025

Sargassum, the stinky, slimy seaweed, is already swarming South Florida beaches, and scientists say a gigantic new bloom of the weed has recently been seen lurking in the tropical Atlantic Ocean. —Rebecca Morin, USA Today, 1 May 2025

Kelp can inspire Almost 200 years ago, the photographer Anna Atkins showed us that art and seaweed science could intertwine, capturing the fleeting beauty of marine life in deep-blue cyanotypes. —Avery Schuyler Nunn, Smithsonian Magazine, 30 Apr. 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)