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

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Etymology

Origin of seaweed

First recorded in 1570–80; sea + weed ¹

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Compare meaning

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

• algae vs. seaweed

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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

"I've been fishing here since I was a boy," said Venkatasamy Kalimuththu, 65, looking disappointedly at the catch -- a few good fish, some small fry, and several clumps of seaweed.

From Barron's ● Oct. 25, 2026

The five-term senator said the categories of products receiving exemptions include corrugated paper cartons, plastic boxes, plastic bags, refrigeration and freezing equipment, packing and wrapping machinery, and seaweed and algae products.

From MarketWatch ● Oct. 23, 2026

Dr Sim says the dog is always right when pointing out a sea squirt, which can be difficult to spot, looking like slime among seaweed and on structures like pontoons and oyster cages.

From BBC ● Oct. 14, 2026

Researchers have identified potential alternatives — including seaweed, cassava waste, single-cell proteins produced by fungi and even sewage.

From Los Angeles Times ● Oct. 9, 2026

He made a hammock of grass fibers and swung himself in it by pulling on a rope, swaying from side to side like seaweed on the rolling sea, full of vacant wonder.

From "Abel's Island" by William Steig

When coral reefs are damaged or lost, the impact goes beyond visible marine life such as fish, sponges, and seaweeds.

From Science Daily ● May 8, 2026

These fossils are among the earliest known seaweeds in the geological record, dating to a time when most organisms were visible only under a microscope.

From Science Daily ● Nov. 18, 2025

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

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

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Related Words

• algae

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