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

Below the surface of the water, species such as green-brown bladderwrack seaweed provide vital functions for other wildlife.

From Barron's ● Aug. 27, 2026

One option is Hawaii’s small but promising ocean-tech industry, which includes firms that repair cargo ships, make sensors to detect floods, breed commercial shellfish or make livestock supplements from seaweed.

From The Wall Street Journal ● Aug. 20, 2026

Even chicken feathers, seaweed and algae were on the list.

From The Wall Street Journal ● Aug. 3, 2026

Macroalgae such as seaweed can have both beneficial and harmful effects, according to Hu.

From Science Daily ● Aug. 3, 2026

Nathan was happy when Mother Water Monster stopped near a bed of rocks that nested on a tangle of seaweed.

From "Healer of the Water Monster" by Brian Young

The scientific divers who found the sample were mapping and analysing seaweeds to check on the health of Cornish maerl beds, a project organised by Natural England.

From BBC ● Jul. 31, 2026

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

From BBC ● Aug. 28, 2025

Bladder, toothed and spiral wracks often have notably higher antioxidant contents than many other seaweeds.

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

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