frustum

noun2

1. •
   A cone or pyramid whose tip has been truncated by a plane parallel to its base.

   • Come, every frustum longs to be a cone, And every vector dreams of matrices. — 1974
2. •
   A portion of a sphere, or in general any solid, delimited by two parallel planes.

   • In some women it^([the os uteri]) is flat, in many more tuberose, and forming, as it were, a frustum of a sphere;[…]. — 1840