From Latin 'volvere' (to turn) — the arched ceiling is 'the turned thing,' kin to 'revolve' and 'evolve.'
An arched structure forming a ceiling or roof in a building; also a secure room or chamber used for storage, especially of valuables; as a verb, to leap over something using the hands or a pole.
From Old French 'voute, volte' (vault, arch), from Vulgar Latin *volvita (a turn, an arch), from Latin 'volvere' (to turn, to roll). The vault is etymologically 'the turned thing' — an arch is a curve, and a curve is a turn. The same Latin verb produced 'revolve,' 'evolve