voussoir

Etymology

Borrowed from French voussoir, from Old French vosoir, from Vulgar Latin *volsorium, from *volsus, from Latin volvō (“I roll”).

noun

1. (architecture) One of a series of wedge-shaped bricks or stones forming an arch or vault.
   It is the voussoir depth in a real arch which enables the arch to carry wider ranges of loading; a large number of different idealized centre-line arches can be contained within a given practical profile. ...[T]his must be so, or no mediaeval bridge would have survived its decentering. 1977, Jaques Heyman, Equilibrium of Shell Structures, Clarendon Press, Oxford, page 2
   Other areas have mortar joints missing, including between the voussoir blocks forming the edge of the arches on either side of the pier. May 20 2020, Philip Haigh, “Ribblehead: at the heart of the S&C's survival and its revival: Ribblehead Viaduct repairs”, in Rail, page 26