pentagonal

adj

1. Of, relating to, or shaped like a pentagon.

   “If the base be a triangle, it is called a triangular prism; if a square, a square prism; if a pentagon, a pentagonal prism; and' if the base is any irregular figure, it is called an irregular prism : ...”

   “Seed micromorphology:—Seed coat is laticostate. Epidermal cells are elliptical to irregularly pentagonal. Cell walls are thickened mostly at the corners, the boundaries are raised […]”

noun

1. Something having the shape of a pentagon.

   “Speaking of protection, note that not only are the end pentagonals surrounded by a generous air space, but the entire instrument is insulated, […]”

   “The pentagonals with the flowers and the leaves of the central calyx are gilded all over, as is the inner lip of the vessel.”