1) Concave 2) Cotyloid 3) Cotyloidal 
(socket) ne: acetabulum the deep socket cup or cavity on the side of the hip bone in which the head of the thigh bone fits to form the hip joint
• (a.) Cup-shaped; saucer-shaped; acetabuliform.
Relating to the acetabulum. ... (05 Mar 2000) ... 
(as″ә-tab´u-lәr) pertaining to the acetabulum.
Ac`e·tab'u·lar adjective Cup-shaped; saucer-shaped; acetabuliform. 
Type: Term Pronunciation: as-ĕ-tab′yū-lăr Definitions: 1. Relating to the acetabulum.
Acetabular: Pertaining to the acetabulum, the cup-shaped socket of the hip joint which is a key feature of the pelvis. The head (upper end) of the femur (the thighbone) fits into the acetabulum and articulates with it, forming a ball-and-socket joint.The acetabulum is not just cup-shaped. The word 'acetabulum' in Latin means cup, a vinegar cup.
[adj] - of the cup-shaped socket that receives the head of the thigh bone
cotyloid adjective of the cup-shaped socket that receives the head of the thigh bone