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

Aside from including two types of hyaluronic acid, Japanese miru seaweed, volcanic marine ferment, and snow mushrooms, all of which boast anti-inflammatory and anti-oxidant properties. —Kiana Murden, Vogue, 29 Jan. 2026

Chef Annie Ng hosts this event that includes the Phoenix ramen bowl for $18 that features shoyo broth topped with seitan, corn, bean sprouts, green onions, bamboo shoots, a soft egg and seaweed, with an optional upgrade with king oyster and shiitake mushrooms for $5. —Lucia Cheng, Des Moines Register, 28 Jan. 2026

Salt & Stone Hand Cream, A fast-absorbing daily hand moisturizer infused with seaweed extracts and antioxidant-rich botanicals to leave skin soft and hydrated. —Essence, 27 Jan. 2026

Spa treatments incorporate seaweed and other local ingredients. —Condé Nast, Condé Nast Traveler, 23 Jan. 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)