Definition of protopyramid in English:

protopyramid

noun

Crystallography
  • The primitive pyramid of a crystal system, in which the horizontal axes of the system intersect the edges of the pyramid (as opposed to one in which the axes intersect the faces midway between the edges).

Origin

Late 19th century; earliest use found in The Century Dictionary.

Pronunciation

protopyramid

/ˌprəʊtə(ʊ)ˈpɪrəmɪd/