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

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Etymology

Origin of deltoid

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

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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

He was expected to begin a rehab assignment this week until he felt discomfort in his right deltoid during a throwing session.

From Seattle Times ● May 9, 2023

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

From Washington Times ● Aug. 24, 2022

The deltoid, the thick muscle that creates the rounded lines of the shoulder is the major abductor of the arm, but it also facilitates flexing and medial rotation, as well as extension and lateral rotation.

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

Another person with well-defined deltoids and pecs and a rapidly shrinking midsection.

From Washington Post ● Apr. 19, 2017

Another effective form of holding is to shoot the hands and grab the outside of the shoulder pads, just over the deltoids.

From Slate ● Sep. 13, 2012

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

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Related Words

• trilateral

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