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.
Anatomy. pertaining to or involving the deltoid.
Also, deltoidal. in the shape of a Greek capital delta (Δ); triangular.

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

subdeltoid, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
deltoid (ˈdɛltɔɪd)
1.  the thick muscle forming the rounded contour of the outer edge of the shoulder and acting to raise the arm
2.  shaped like a Greek capital delta, Δ; triangular
[C18: from Greek deltoeidēs triangular, from delta]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin & History

1741, in deltoid muscle, from Gk. deltoeides "triangular," lit. "shaped like the letter delta;" see delta + -oid.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

deltoid del·toid (děl'toid')

  1. Of or relating to the deltoid muscle.

  2. Triangular in shape or outline.

The deltoid muscle.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Britannica


large, triangular muscle that covers the shoulder and serves mainly to raise the arm laterally. The deltoid, as it is commonly known, originates on the outer front third of the clavicle (collarbone) and the lower margin of the spine of the scapula (shoulder blade). Its fibres unite to form a thick tendon that inserts at the deltoid tuberosity, a rough spot above the middle of the outer surface of the humerus (upper arm bone).

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Bogans underwent successful surgery to repair a fractured left ankle and torn deltoid ligament before getting released.
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