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

Ling’s blue ink drawings on paper conjure horses, too, but the lines are more spare, moving like seaweed, or long, thick hair, under water. —Samantha Conti, WWD, 20 Feb. 2025

Iodine is in foods such as fish, seaweed (including nori and wakami), and eggs.1415 A Quick Review Himalayan and sea salt contain various essential minerals, but most are only present in trace amounts, offering little health benefit within the confines of safe salt consumption. —Lauren O'Connor, Ms, Health, 18 Feb. 2025

Many products are available and organic formulations are often made from seaweed or kelp. —Joshua Siskin, Orange County Register, 14 Feb. 2025

For this study, the research team looked at marine fungi found in corals, seaweed, sand, and sponges from Hawai’i’s nearshore. —Monica Cull, Discover Magazine, 14 Feb. 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)