What Persian architectural feature is a large vaulted chamber with a pointed-arch opening, first used as an entrance to royal reception halls in Persian palaces, and later adapted to mosque designs?

Muqarnas

Explanation:

Muqarnas is a form of ornamented architectural vaulting. In Iranian architecture, it is known as Ahoopāy.

It is sometimes called honeycomb vaulting because of the design resembling honeycomb shape and form. The purpose of using muqarnas is to smoothly transition from structural elements to decorative zones in architecture. It is used for arches, domes, cornices, and vaults, and is often used in the design of mihrab of the mosques.