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

For a true picture of the Outer Banks before electricity and running water, Anderson-Silver nods to My Daily Bounded Realm by Robin Daniels Holt, which takes readers back to a time when locals on Hatteras Island made a living through selling seaweed for mattress stuffing and ate molecrab stew. —Kat Chen, Condé Nast Traveler, 25 Apr. 2026

The key appeal is the opportunity to meet suppliers, from farmers to seaweed foragers, as well as culinary ambassadors and chefs, such as Máret Ravdna Buljo, whose mission is to reinvigorate Indigenous Sámi culinary culture. —Karen Gardiner, Travel + Leisure, 25 Apr. 2026

The Southeast coast and the Florida Keys are usually most heavily impacted by clumps of sargassum washing ashore, and the stenchy seaweed has already been cropping up in places like Cocoa Beach and Miami Beach throughout the month of April. —Sarah Perkel, USA Today, 22 Apr. 2026

Scientists monitored seawater, fish and seaweed to track how radioactive materials moved and changed over time. —Eduardo B. Farfán, The Conversation, 21 Apr. 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)