The Collaborative International Dictionary
Archivolt \Ar"chi*volt\, n. [F. archivolte, fr. It. archivolto; pref. archi- + volto vault, arch. See Vault.] (Arch.)
The architectural member surrounding the curved opening of an arch, corresponding to the architrave in the case of a square opening.
More commonly, the molding or other ornaments with which the wall face of the voussoirs of an arch is charged.
Wiktionary
n. (context architecture English) An ornamental molding or band following the curve on the underside of an arch.
Wikipedia
An archivolt (or voussure) is an ornamental molding or band following the curve on the underside of an arch. It is composed of bands of ornamental moldings (or other architectural elements) surrounding an arched opening, corresponding to the architrave in the case of a rectangular opening. The word is sometimes used to refer to the under-side or inner curve of the arch itself (more properly, the intrados).
Usage examples of "archivolt".
It was a fore building with an archivolt of roses in base relief that curved over glistening white, stone steps, longer at the bottom than top.
These glazed brick or tiles, with figured designs, were fixed upon the walls, arches, and archivolts by bitumen mortar, and made up the first mosaics of which we have record.
This led to the enrichment of the archivolts and imposts with that peculiar type of conventional foliage which characterizes Mahommedan work, and which in this case was carried out by Coptic craftsmen.