sea urchin

American  

noun

sea urchins plural

1. any echinoderm of the class Echinoidea, having a somewhat globular or discoid form, and a shell composed of many calcareous plates covered with projecting spines.

2. a tall evergreen shrub or small tree, Hakea laurina, of Australia, having narrow leaves and dense, globe-shaped clusters of crimson flowers with long yellow stamens.

---

sea urchin British  

noun

1. any echinoderm of the class Echinoidea, such as Echinus esculentus ( edible sea urchin ), typically having a globular body enclosed in a rigid spiny test and occurring in shallow marine waters

---

Other Word Forms

Noun Inflected Forms

• sea urchins
  plural

Etymology

Origin of sea urchin

First recorded in 1585–95

Example Sentences

Her fossilized sea urchin, from a beach on the Red Sea, “responds by radiating its own inner joy at being found and loved too,” whispering: “We are two cyclical beings, each with their own story.”

From The Wall Street Journal • Jan. 16, 2026

When sea urchin populations grow too large, however, especially if their natural predators are heavily hunted or overfished, the balance can flip.

From Science Daily • Dec. 12, 2025

Yama Seafood Uni – The first time I tried uni — sea urchin — was at Shiro’s in Seattle.

From Salon • Dec. 4, 2025

Not to mention, you could step on a stingray or a sea urchin.

From Los Angeles Times • Oct. 16, 2024

Thicknesse had fallen to the ground with tiny spikes erupting all over him; he seemed to be turning into some form of sea urchin.

From "Harry Potter and the Deathly Hallows" by J.K. Rowling