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

For the second straight day, Servais said he had no updates on the progress of reliever Andres Munoz and his recovery from a right deltoid strain.

From Seattle Times ● Apr. 29, 2023

Mariners: LF Sam Haggerty is dealing with an isolated deltoid strain but is progressing, manager Scott Servais said.

From Washington Times ● Aug. 24, 2022

A common example is the deltoid muscle of the shoulder, which covers the shoulder but has a single tendon that inserts on the deltoid tuberosity of the humerus.

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

The vast majority of these “T-maxxing” posts were made by influencers with zero medical or scientific expertise, but that doesn’t matter because their deltoids are outstanding.

From The Wall Street Journal ● Sep. 12, 2026

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

That’s despite Linda Hamilton returning to the franchise for the first time since 1991’s Terminator 2, plus Mackenzie Davis and her deltoids.

From Slate ● Nov. 3, 2019

And there was Soboroff, a Los Angeles civic leader and aide to a former mayor, offering sympathy and camaraderie by soothing McCourt’s tense deltoids.

From New York Times ● Dec. 31, 2011

He was wiry, with developed deltoids and lats: possibly a rock climber, definitely not a weight-room guy.

From "Genuine Fraud" by E. Lockhart

Related Words

• trilateral