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

Example Sentences

Also unearthed were fireplaces containing evidence of the burning of toothed wrack seaweed to form soda ash.

From BBC • Mar. 25, 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

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

He is wrapping rice and little anchovies in my favorite kim, little flat squares of salty, crispy seaweed, and says “ah” to me.

From "Finding Junie Kim" by Ellen Oh

Related Words

• algae