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 the menu will certainly make any meat-lover rejoice (there is Australian wagyu and a black diamond prime Tomahawk steak), those in the mood for something lighter also have plenty of options, such as a Dover sole in seaweed hollandaise and a whole roasted branzino. —Nneka M. Okona, Travel + Leisure, 15 Feb. 2026

A la carte items include Baja oysters, Black Hat Bakery sourdough, a daily ceviche selection and the Carter Country Regenerative Beef cheeseburger with seaweed aioli and beef tallow fries. —Pam Kragen, San Diego Union-Tribune, 10 Feb. 2026

The alcohol-free formula doubles as a hydrating mist thanks to a blend of hyaluronic acid, glycerin, and seaweed extract. —Conçetta Ciarlo, Vogue, 9 Feb. 2026

This version of the Hawaiian snack — buttery and tossed with seaweed and sesame seeds — is adapted from food stylist Caroline Hwang’s recipe, which was passed to her from her friend, Corey Chow, former chef de cuisine at Per Se in New York, who adapted it from his mom. —Los Angeles Times, 8 Feb. 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)