(ˈ)vü|swär noun
( -s )
Etymology: French, from (assumed) Vulgar Latin volsorium, from volsus (alteration of Latin volutus, past participle of volvere to roll, turn) + Latin -orium -ory — more at voluble
: one of the tapering or wedge-shaped pieces forming an arch or vault — compare intrados , keystone , springer