gluteus maximus

The gluteus maximus is the largest and most superficial of the three gluteal muscles. It makes up a large portion of the shape and appearance of the buttocks.It is a broad and thick fleshy mass of a quadrilateral shape, and forms the prominence of the nates. Its large size is one of the most characteristic features of the muscular system in humans, connected as it is with the power of maintaining the trunk in the erect posture.
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Gluteus max·i·mus n. A muscle with origin from the ilium, the sacrum and the coccyx, and the sacrotuberous ligament, with insertion to the [more]Gluteus maximus - Community and Resources

Noun
1. the outermost of the three gluteal muscles
(hypernym) gluteus, gluteus muscle, gluteal muscle, glute