acetabulum

Definitions

(Noun) (1) cup-shaped socket in pelvic girdle for head of femur, forming the hip joint in tetrapod vertebrates; (2) in insects, thoracic cavity in which the leg is inserted; (3) socket used of coxa in arachnids; (4) sucker used for attachment in flukes, tapeworms, and leeches; (5) sucker on arm of cephalopod

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socket in the hip bone that the femur fits into (the hip joint)