The Collaborative International Dictionary of English v.0.48:

Basisphenoid \Ba`si*sphe"noid\, Basisphenoidal
\Ba`si*sphe*noid"al\, a. [Basi- + sphenoid.] (Anat.)
   Of or pertaining to that part of the base of the cranium
   between the basioccipital and the presphenoid, which usually
   ossifies separately in the embryo or in the young, and
   becomes a part of the sphenoid in the adult.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Basisphenoid \Ba`si*sphe"noid\, n. (Anat.)
   The basisphenoid bone.
   [1913 Webster]