frustoconical

frustoconical = of the shape of a frustum of a cone

plural: ‘frustums’ or ‘frusta’ 
: the basal part of a solid cone or pyramid formed by cutting off the top by a plane parallel to the base
also : the part of a solid intersected between two usually parallel planes

src: https://www.merriam-webster.com/dictionary/frustoconical

Frustoconical: The Right Word for the Right Shape

Another unusual pair of words that are common only in a patent attorney’s lexicon are frustoconical and frustopyramidal, meaning truncated cone and truncated pyramid, respectively. Frustoconical appears in the claims fo 8432 patents since 1976, frustopyramidal in only 80 patents since 1976.

If you need to describe the shape of a truncated cone, frustoconical is exactly what you need to use. Even though the work is obscure, it is doubtful that it is any harder for a lay person to understand than “truncated cone” than frustoconical.

(https://www.harnessip.com/blog/2015/12/22/frustoconical-the-right-word-for-the-right-shape/)

U.S. Patent No. 8,534,460, Fig. 2 showing a “tapering frustoconical sidewall 32”