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

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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

Targets the core, pectorals, deltoids, and triceps. SELF, "A 15-Minute No-Equipment Core Workout You Can Do at Home," 18 Jan. 2019 The rolling out movement primarily works your lats and deltoids, whereas the second half of the movement—the rolling in portion—really targets your core, specifically your rectus abdominis, says Brewer. Jenny Mccoy, SELF, "Why the Ab Wheel Is Such a Challenging and Effective Workout Tool," 6 Dec. 2018 Deadlifts already work the posterior chain, or the muscles at the rear of the body like the hamstrings, gluteus maximus, trapezius, posterior deltoids, and erector spinae. Leah Prinzivalli, SELF, "Why the Deficit Deadlift Is a Great Modification for Beginners," 5 Dec. 2018 Shots given in muscles — like the deltoid in the upper arm where flu shots are usually given — tend to be more painful than ones that aren't injected into the muscle, Stewart said. Erica Sweeney, Teen Vogue, "Why Do Some Vaccines Hurt More Than Others?," 24 Oct. 2018 Then, the overhead press portion adds upper-body work, requiring strength from your anterior and posterior deltoids (front and back of the shoulders), biceps, and triceps, says Mansour. Jenny Mccoy, SELF, "Strengthen Your Entire Body With This 1 Compound Exercise Move From Jennifer Garner’s Trainer," 23 May 2018 This move targets your pecs, deltoids, biceps, hamstrings, core, and glutes, says De La Rue. Jenny Mccoy, SELF, "Strengthen Your Shoulders and Core With This Plank Workout From Jennifer Garner’s Trainer," 30 Apr. 2018 The heart-like shape of the model’s left deltoid, or shoulder muscle, corresponds to the shape of the group of small muscles at the base of the model’s thumb, adjoining the palm. Catesby Leigh, National Review, "A Genius in Draft Form," 20 Jan. 2018 Muscles Used: Thenar thumb muscles, forearm, deltoid. J.r. Havlan, Esquire, "Get as Fit as the Donald with Trumpercise!," 12 Oct. 2016

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

The first known use of deltoid was circa 1681

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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

More from Merriam-Webster on deltoid

Rhyming Dictionary: Words that rhyme with deltoid Encyclopedia article about deltoid

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concealment of treason or felony

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