acetabulum

n. hipbone socket (Anatomy); cup shaped form (Zoology)

The acetabulum is a surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
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Acetabulum /ac·e·tab·u·lum/ pl. aceta´bula [L.] the cup-shaped cavity on the lateral surface of the hip bone, receiving the head of the femur. [more]Acetabulum - Community and Resources

Noun
1. the cup-shaped hollow in the hipbone into which the head of the femur fits to form a ball-and-socket joint
(synonym) cotyloid cavity
(hypernym) socket
(part-holonym) hipbone, innominate bone

n. (Anatomy) acetabulum, hipbone socket; (Zoology) cup shaped form