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

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

“Experiences like seaweed foraging invite travelers to slow down, engage with the natural environment and learn directly from local experts, creating a deeper emotional connection to the destination.”

From Salon • Mar. 14, 2026

Kim Namin, 29, runs a seasoned gim processing factory with a 30-year family history in Wando, an island in South Korea's southern waters known for abalone and seaweed production.

From BBC • Feb. 4, 2026

In 2023, US supermarket chain Trader Joe's Gimbap - a Korean rice roll wrapped in seaweed - went viral and was cleared off the shelves nationwide shortly after its launch.

From BBC • Feb. 4, 2026

Dicey gathered an armload of damp seaweed from the water’s edge.

From "Homecoming" by Cynthia Voigt

Related Words

• algae