seaweed

American  

[see-weed] / ˈsiˌwid /

noun

seaweeds plural

1. any plant or plants growing in the ocean.

2. a marine alga.

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seaweed British  

/ ˈsiːˌwiːd /

noun

1. any of numerous multicellular marine algae that grow on the seashore, in salt marshes, in brackish water, or submerged in the ocean

2. any of certain other plants that grow in or close to the sea

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seaweed Scientific  

/ sē′wēd′ /

1. Any of various red, green, or brown algae that live in ocean waters. Some species of seaweed are free-floating, while others are attached to the ocean bottom. Seaweed range from the size of a pinhead to having large fronds (such as those of many kelps) that can be as much as 30.5 m (100 ft) in length. Certain species are used for food (such as nori) and fertilizer, and others are harvested for carrageenan and other substances used as thickening, stabilizing, emulsifying, or suspending agents in industrial, pharmaceutical, and food products. Seaweed is also a natural source of the element iodine, which is otherwise found only in very small amounts.

2. See more at brown alga green alga red alga

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Other Word Forms

Noun Inflected Forms

• seaweeds
  plural

Etymology

Origin of seaweed

First recorded in 1570–80; sea + weed ¹

Compare meaning

How does seaweed compare to similar and commonly confused words? Explore the most common comparisons:

• algae vs. seaweed

Explanation

What is a type of algae that we sometimes eat? Seaweed! Yes, if you have ever eaten a sushi roll, you've most likely eaten seaweed. If you've ever been to the beach, you've seen seaweed on the sand and growing from rocks in and near the water. Seaweed can be classified as red, brown, or green algae, and many types are harvested and used for food. In sushi, rice and fish are wrapped in seaweed, and another seaweed, called carrageenan, is a common additive that thickens foods like ice cream and yogurt and products like toothpaste.

Example Sentences

See Examples For:

seaweed seaweeds

Officials are required by the state constitution to let the public swim, fish and collect seaweed along the state’s 400 miles of coastline.

From The Wall Street Journal ● Jul. 8, 2026

The coastal waters are used by tribal people for seaweed and abalone gathering, and the shores host youth cultural camps, he said.

From Los Angeles Times ● Jul. 3, 2026

Unfazed by the crashing waves, 72-year-old Wu Feng-chiao yanks fistfuls of brownish-purple seaweed she will process into jelly, one of the last women in Taiwan keeping the marine harvest tradition alive.

From Barron's ● Jun. 30, 2026

At first glance, it looked like a small raft of seaweed.

From Slate ● Jun. 19, 2026

The Berserker had seaweed strung through one of his golden earrings, and he was wheezing.

From "Impossible Creatures" by Katherine Rundell

It said the site supported specialised communities of animals, seaweeds and the rare short-snouted seahorse.

From BBC ● Aug. 28, 2025

The seaweeds with the greatest nutritional value include those often referred to as the "wracks".

From Salon ● Aug. 5, 2024

I mentioned some of them before — the seaweeds, the mushrooms, legumes, and so on.

From Los Angeles Times ● Jul. 18, 2024

There are approximately 10,000 different species of seaweeds in the world, however only 145 species are eaten today, principally in Asia.

From Science Daily ● Oct. 17, 2023

Japanese waters are also rich in clams and oysters and other shellfish, crabs and shrimp and crayfish, and edible seaweeds.

From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond

Related Words

• algae