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

Maerl beds may closely resemble corals but they are in fact thousands of pieces of free-living calcified seaweed that can interlock to create a carpet brimming with life.

From BBC ● Jul. 31, 2026

Park and study co-corresponding author Woo-Jae Kim, a professor of chemical engineering and materials science at Ewha Womans University, originally developed the process as a carbon-neutral way to produce hydrogen from biomass such as seaweed.

From Science Daily ● Jul. 31, 2026

Mexico is deploying specialized navy ships to fight a massive influx of sargassum on the country's Caribbean beaches, authorities said Thursday, as the smelly seaweed threatens the crucial tourism sector.

From Barron's ● Jul. 30, 2026

The recipes are interspersed with stories from Kwon’s childhood in the store and illustrated spreads devoted to ingredients such as seaweed and tofu, explaining their varieties, particular virtues and best uses.

From Salon ● Jul. 23, 2026

Under the water I kept my eyes shut and touched the sandy bottom with my hands and feet and felt a couple slimy seaweed limbs brush over my back and legs.

From "We Were Here" by Matt De La Peña

For humans, the abundant minerals and anti-inflammatory properties of certain seaweeds have seen their extracts used in medicines from treating acid reflux to wound dressings.

From BBC ● Jul. 31, 2026

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

“And it was, like, this butter board that had crab and preserved lemon and these seaweeds and all this stuff and then, like, this brown butter, as well, on top of the butter.”

From Salon ● Apr. 1, 2025

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