deltoid

American  

[del-toid] / ˈdɛl tɔɪd /

noun

• deltoids
  plural

1. Anatomy. a large, triangular muscle covering the joint of the shoulder, the action of which raises the arm away from the side of the body.

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adjective

1. Anatomy. pertaining to or involving the deltoid.

2. Also in the shape of a Greek capital delta (Δ); triangular.

deltoid British  

/ ˈdɛltɔɪd /

noun

1. the thick muscle forming the rounded contour of the outer edge of the shoulder and acting to raise the arm

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adjective

1. shaped like a Greek capital delta, Δ; triangular

Other Word Forms

Derived Forms

• subdeltoid
  adjective

Inflected Forms

Nouns

• deltoids
  plural

Etymology

Origin of deltoid

1675–85; < Greek deltoeidḗs delta-shaped, equivalent to délt ( a ) delta + -oeidēs -oid

Explanation

Your deltoid is your shoulder muscle — it makes up the rounded part of your shoulder and allows you to twist, raise, and extend your arms. When deltoid is used as an adjective, it means "triangular," so you could describe your A-frame house or pup tent as deltoid. The deltoid muscle got its name because of its triangular shape and its three distinct sections of muscle fibers. Weight lifters and body builders sometimes call these muscles "delts" for short. Deltoid comes from the Greek deltoeides, "triangular," or "shaped like the Greek letter delta."

Example Sentences

See Examples For:

deltoid deltoids

All of the X-Men were strong, their muscles etched from deltoid to abdomen to quadriceps.

From Slate ● Jul. 29, 2023

Servais had no update on reliever Andres Munoz, who is still working his way back from a deltoid strain in his right shoulder.

From Seattle Times ● May 5, 2023

Mariners: LF Sam Haggerty received an MRI, revealing an isolated deltoid strain.

From Washington Times ● Aug. 24, 2022

The deltoid ligament supports the ankle joint and also resists excessive eversion of the foot.

From Textbooks ● Jun. 19, 2013

They would aim for the muscle that Tariq, in a professorial voice, called the deltoid.

From "A Thousand Splendid Suns" by Khaled Hosseini

Johnson, squeezed into a wig so tight we get a vicarious headache, has pumped up his deltoids to nearly reach his prosthetic cauliflower ears.

From Los Angeles Times ● Oct. 3, 2025

Last summer, when photos from the set of Terminator: Dark Fate showed Mackenzie Davis sporting a fashion bowl cut, grimy tank top, and massive deltoids, lesbian Twitter lost its mind.

From Slate ● Nov. 1, 2019

You hope this pleasant-seeming youth has a career to match the size of his deltoids and his daddy’s mouth.

From Washington Post ● Apr. 29, 2019

But the longer I was there, the more I seemed to thrive under the limitations, enjoying the pull in my deltoids as I beat things by hand.

From The Guardian ● Nov. 18, 2018

When you see someone waving her arms, the first thing you want to know is whether she is trying to attract attention, shoo away flies, or exercise her deltoids.

From "The Sense of Style" by Steven Pinker

Related Words

• trilateral