What architectural term describes a single room shop covered by a barrel vault?

The term that describes a single room shop covered by a barrel vault is "taberna." In ancient Roman architecture, a taberna was typically a small, single-room space, often used as a shop or a workshop. The barrel vault, which is a continuous series of arches forming a tunnel-like structure, provided an effective means of roofing these spaces while allowing for greater interior heights and unencumbered interiors. This design was practical for both commercial and residential purposes.

By contrast, the other terms presented do not refer to this specific architectural form. "Pumice" is a type of volcanic rock that can be used in construction for lightweight materials, but it does not describe a room or architectural form. "Spandrel" refers to the space between the arches and areas above doorways or windows, which is more concerned with structural elements rather than a specific room type. A "theater," on the other hand, typically refers to a large audience space designed for performances and would not pertain to the characteristics of a single-room shop. Thus, "taberna" is the most accurate term to denote a small shop with a barrel vaulted ceiling in the context of ancient architecture.