Definition of deltoid in US English:



  • 1Triangular.

    ‘a tree with large deltoid leaves’
    • ‘Farther distally around the middle part of the shaft, is the deltoid tuberosity along the lateral border.’
    • ‘Specimens are members of the Hyperoblastidae based on presence of four spiracles and anispiracle, deltoid crests (not faces), and two to four anideltoids.’
    • ‘In some cases, the deltoid branch of the profunda brachii (16% of individuals) arises from the brachial or from the superior ulnar collateral.’
    • ‘The spiracles in orbitremitids pierce the adoral extremity of deltoid faces and are bounded laterally by ambulacral plates, which is the condition seen in the Chinese specimens.’
    1. 1.1 Denoting a thick triangular muscle covering the shoulder joint and used for raising the arm away from the body.


  • 1A deltoid muscle.

    • ‘What's more, it builds what powerlifters call ‘accessories’: biceps, triceps, deltoids, abs and other vanity muscles.’
    • ‘During surgery, we observed partial or complete detachment of the trapezoid and deltoid muscles from the lateral clavicle in all patients.’
    • ‘The skin over the deltoid muscle or posterior arm is the most common vaccination site.’
    • ‘Performed with or without assistance, pull-ups are a great way to strengthen the muscles of the upper body, particularly the latissimus dorsi, posterior deltoids and biceps.’
    • ‘Arms too far back reduces stress on the posterior deltoids and involves the trapezius and back muscles.’
    • ‘The cable crossover works the pectoralis major and minor, anterior deltoid, coracobrachialis and serratus anterior.’
    • ‘Feel the three distinct heads of each deltoid contract and relax.’
    • ‘The trapezius may send a fascicle to the sternum and to the deltoid muscle.’
    • ‘My deltoid muscles are too thick, it hurt to even try this new streamline.’
    • ‘After getting eight to 12 reps, lie on your left side to work your right medial deltoid.’
    • ‘This is why each deltoid is made up of three heads, each of which has a separate function.’
    • ‘The intramuscular vaccine should be administered in the deltoid muscle and can be administered with other vaccines.’
    • ‘He subsequently developed weakness in the deltoid, infraspinatus and supraspinatus muscles.’
    • ‘These vaccines are inactivated and should be administered intramuscularly into the deltoid muscle.’
    • ‘Results of a comparison of the noninjured and the injured shoulder in the patient group showed that on both sides the deltoid muscle is active significantly earlier than the trapezius muscle.’
    • ‘If gravity were reduced or absent the deltoid's tension would raise the arm.’
    • ‘In many cases this is due to a genetic propensity of the deltoid and tricep muscles to be primarily involved in this pushing motion.’
    • ‘Tendinitis of the deltoid muscle tendon was ruled out as well.’
    • ‘Evidence of a therapeutic effect can be seen by strengthening of the deltoid muscle on repeat muscle testing.’
    • ‘Strength training targeted 5 muscle groups (latissimus dorsi, pectorals, triceps / deltoid, hamstrings, and quadriceps).’
    • ‘Raise your arms out to your sides with your elbows slightly bent and wrists turned in, making sure not to use anything but your deltoids to raise the weight.’
    • ‘This shoulder program focuses on the big, powerful deltoid as well as the smaller muscles that make up the rotator cuff.’
    • ‘The most common substitution muscles are the biceps, triceps, deltoid and neck muscles.’
    • ‘For example, if you're going to do heavy shoulder presses, you'll be using more than just your deltoids and triceps; the neck and trapezius muscles will be stressed as well.’
    • ‘The desired injection site is the outer aspect of the upper arm, midway between the shoulder and the elbow in the groove between the deltoid and triceps muscles.’
    1. 1.1 Each of the three parts of a deltoid muscle, attached at the front, side, and rear of the shoulder.
      ‘the anterior deltoid’
      • ‘One key to shoulder training is to think of your front, side and rear deltoids as distinct (but small) muscles.’
      • ‘This works the trapezius and front deltoids together.’
      • ‘The heavier you can go with your bench-press sets, the better for your pectorals, anterior deltoids and triceps, provided their work is not being stolen by cheating.’
      • ‘The rear deltoid, teres minor and infraspinatus are responsible.’
      • ‘The front deltoids and the triceps are recruited as secondary muscles.’
      • ‘Hold your shoulders low, so that only your anterior deltoid, not your trapezius, performs the lift.’


Mid 18th century: from French deltoïde, or via modern Latin from Greek deltoeidēs.