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

In a Facebook group with more than 17,000 members dedicated to discussing Florida’s sargassum, travelers regularly debate whether to keep or change their plans to avoid the rotten-egg-smelling seaweed. —Ashley Miznazi, Miami Herald, 9 May 2026

From Natura Bissé facials, to hot river stone massages, to detoxifying seaweed wraps, time truly stops within these walls. —Condé Nast, Condé Nast Traveler, 7 May 2026

There is no rice, no seaweed salad — simply the fish — which spotlights the ahi’s quality. —Stephanie Breijo, Los Angeles Times, 7 May 2026

The program, known as MARINER — Macroalgae Research Inspiring Novel Energy Resources — consisted of projects ranging from developing heat-resistant kelp strains that can withstand warming oceans to studies on seaweed genomes. —ABC News, 6 May 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)