del·​toid | \ ˈdel-ˌtȯid How to pronounce deltoid (audio) \

Definition of deltoid

 (Entry 1 of 2)

: a large triangular muscle that covers the shoulder joint and serves to raise the arm laterally



Definition of deltoid (Entry 2 of 2)

1 : having a triangular shape a deltoid leaf — see leaf illustration
2 : relating to, associated with, or supplying the deltoid

Did you know?

The fourth letter of the Greek alphabet is delta, and a capital delta is triangle-shaped. In English, delta commonly means the sand deposits that form a huge triangle at the mouth of certain large rivers. Deltoid as an adjective means "having a triangular shape", and botanists often use the word to describe the shape of certain leaves. The triangular, swept-back wings seen on jet fighter aircraft are called delta wings. Your deltoid muscles—not far from your rhomboids—form a cap on your shoulders, and some gym trainers even treat shoulder and deltoid as synonyms. Can you guess the general shape of deltoids when seen from the side?

Examples of deltoid in a Sentence

Recent Examples on the Web: Noun Therefore, those receiving a vaccine in the thigh may need to use a longer needle (commonly 1.5 inch, as opposed to a 1 inch needle in the deltoid). Lois K. Solomon,, 22 Nov. 2021 Your lateral deltoid, the middle part of your shoulder, helps raise your arms to the side and assists with reaching. Elizabeth Millard, SELF, 1 June 2021 Single doses of Johnson & Johnson vaccine were injected in their arms during the promotional event and then into the somewhat larger deltoid of former Vikings linebacker E.J. Henderson. Jeremy Olson, Star Tribune, 31 Mar. 2021 The shot into her right deltoid brought hope to a country where the virus has infected more than 680,000 people and killed about 17,400 of them. Washington Post, 15 Jan. 2021 This combination of exercises will hit your triceps, biceps, pectoralis muscles, and muscles in the shoulders and upper back, including the rhomboids, deltoids, rhomboids, traps, and lats. Amy Marturana, SELF, 9 Feb. 2019 Van Der Beek’s deltoids and obliques are much more defined after the dance training, possibly from all the twists and lifts. Kelsey Hurwitz, Woman's Day, 2 Dec. 2019 Turay had dislocated his ankle, tore the deltoid ligament in his right ankle and suffered a fracture. Joel A. Erickson, Indianapolis Star, 17 Oct. 2019 The worry is for injury to the syndesmotic ligament that holds the fibula and tibia together, as well as the deltoid ligament. San Diego Union-Tribune, 22 Sep. 2019 Recent Examples on the Web: Adjective During the 2½-hour process, originally expected to take 90 minutes, Anderson took out two screws that shredded the posterior tib tendon in McCormick’s ankle and put in tight rope to secure the deltoid ligaments. oregonlive, 10 Sep. 2021 Women also have thicker fat pads in the deltoid muscle—the part of the upper shoulder where the vaccine is injected. Emily Mullin, Smithsonian Magazine, 20 Apr. 2021 Hey, Paul: Williams revealed in December that his shoulder injury involves damage to the axillary nerve, which helps control the deltoid muscles of the shoulder and the skin around it. cleveland, 7 Feb. 2021 Vaccines are generally injected into the deltoid muscle of the arm. WSJ, 15 Jan. 2021 Just before noon, the first needle hit the left deltoid muscle of registered nurse Katie Walz, who works in the cardiovascular intensive care unit at UCMC. From Usa Today Network And Wire Reports, USA TODAY, 16 Dec. 2020 This exercise gets into the deltoid muscles (the large, triangular muscle occupying the upper arm and the shoulder) and will help loosen up the arms as well. Stephanie Mansour, CNN, 15 Dec. 2020 Her pectoralis major and deltoid muscles, for example, had been used to draw a bow across her chest. Fox News, 30 Nov. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'deltoid.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of deltoid


circa 1681, in the meaning defined above


circa 1753, in the meaning defined at sense 1

History and Etymology for deltoid


New Latin deltoides, from Greek deltoeidēs shaped like a delta, from delta

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Time Traveler for deltoid

Time Traveler

The first known use of deltoid was circa 1681

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Last Updated

1 Dec 2021

Cite this Entry

“Deltoid.” Dictionary, Merriam-Webster, Accessed 2 Dec. 2021.

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More Definitions for deltoid



English Language Learners Definition of deltoid

: a large muscle of the shoulder


del·​toid | \ ˈdel-ˌtȯid How to pronounce deltoid (audio) \

Medical Definition of deltoid

 (Entry 1 of 2)

: a large triangular muscle that covers the shoulder joint, serves to raise the arm laterally, arises from the upper anterior part of the outer third of the clavicle and from the acromion and spine of the scapula, and is inserted into the outer side of the middle of the shaft of the humerus

called also deltoid muscle

— see deltoid tuberosity



Medical Definition of deltoid (Entry 2 of 2)

: relating to, associated with, or supplying the deltoid the deltoid branch of the thoracoacromial artery

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