seaweed

American  

[see-weed] / ˈsiˌwid /

noun

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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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

When I visited Havana again this spring to report on the mounting crisis, the malecón was deserted, strewn with brown seaweed that had been flung from the ocean by crashing waves.

From Los Angeles Times • Apr. 20, 2026

A milk-based dessert similar in appearance to a blancmange, the pudding uses carrageen moss – a type of seaweed found in coastal areas – to give it a gelatinous texture.

From BBC • Apr. 17, 2026

It’s so peculiar that when the guy who long oversaw the process first encountered the sights and noises emanating from the seaweed lab, he questioned his career choices.

From The Wall Street Journal • Mar. 18, 2026

Wind whips hair across your face as you bend over to pick up the perfect bit of seaweed.

From Salon • Mar. 14, 2026

He smiled and picked up another bulb of seaweed.

From "We Were Here" by Matt De La Peña

Related Words

• algae