deltoid

1 of 2

noun

del·​toid ˈdel-ˌtȯid 

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

deltoid

2 of 2

adjective

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

An ankle sprain is less commonly caused by an eversion injury, where the foot turns outward and tears the deltoid ligament (the main stabilizer of the ankle joint) on the inside of the ankle. —Laura Schober, Health, 16 Jan. 2025

Goblet Squat Targets: Legs, glutes, core, biceps and deltoids Repetitions: Eight to 10 Editors’ Picks A Light, Bright Feast for After the Holidays Are These Shoes Hideous or Genius? Video Begin with the kettlebell at chest level. —Hilary Achauer, New York Times, 8 Jan. 2025

Adjective

The trapezius, deltoid, tricep, and bicep muscles were poppin’, and so was her smile. —Victoria Uwumarogie, Essence, 2 Apr. 2025

Chest press targets the pectoral, deltoid, and tricep muscles. —Alyssa Hui, Verywell Health, 28 Apr. 2023

Word History

Etymology

Noun

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

First Known Use

Noun

circa 1681, in the meaning defined above

Adjective

circa 1753, in the meaning defined at sense 1

Medical Definition

deltoid

1 of 2 noun

del·​toid ˈdel-ˌtȯid 

: 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

deltoid

2 of 2 adjective

: relating to, associated with, or supplying the deltoid

the deltoid branch of the thoracoacromial artery