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

Seaweed foraging on the rocky coastline at the edge of the Pacific Ocean can be arduous and dangerous, says Wu, whose passion has kept her going for more than half a century.

From Barron's • Jun. 30, 2026

Seaweed is once again showing promise for making cattle farming more sustainable.

From Science Daily • Dec. 2, 2024

Scobell says the little details of their friendship “hit so much harder” in the live-action adaptation — including the use of the nicknames Seaweed Brain and Wise Girl.

From Los Angeles Times • Jan. 30, 2024

Seaweed is edible, nutritious, sometimes medicinal, abundant and local.

From Salon • Oct. 25, 2023

“Well then, Seaweed Brain? What are you waiting for?”

From "The Sea of Monsters" by Rick Riordan

Related Words

• algae