The Collaborative International Dictionary of English v.0.48:

cotyloid \cot"y*loid\, cotyloidal \cotyloidal\(k?t"?-loid), a.
   [Cotyle + -oid] (Anat.)
   (a) Shaped like a cup; cup-shaped; as, the cotyloid cavity,
       the cup-shaped socket which receives the head of the
       thigh bone.
   (b) Pertaining to a cotyloid cavity; as, the cotyloid
       ligament, or notch.

   Syn: acetabular, cotyloid.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

cotyloidal
    adj 1: of the cup-shaped socket that receives the head of the
           thigh bone [syn: acetabular, cotyloid, cotyloidal]