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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
Max Dible, MSNBC Newsweek, 31 Oct. 2025
Flu shots typically go into the upper arm (specifically the deltoid muscle), which means having a removable layer or avoiding the sweaters altogether might prevent some hassle.
—Khloe Quill, FOXNews.com, 9 Oct. 2025
Victoria Uwumarogie, Essence, 2 Apr. 2025
Chest press targets the pectoral, deltoid, and tricep muscles.
—Alyssa Hui, Verywell Health, 28 Apr. 2023
See All Example Sentences for deltoid
Cite this Entry
“Deltoid.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/deltoid. Accessed 3 Nov. 2025.
Copy CitationMedical Definition
deltoid
1 of 2 noun
called also deltoid muscle
see deltoid tuberositydeltoid
2 of 2 adjective
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