Arch. [a. F. tierceron (1518 in Godef., Compl.), f. tiers, tierce third + suffix -on (see -OON), with intercalated -er-: see Godef. § 63. 1.] A subordinate arch springing from the point of intersection of two main arches of a vault.
1842–76. Gwilt’s Encycl. Archit., Index, Tierceron, in vaulting.
1890. C. H. Moore, Goth. Archit., i. 18, note. The additional ribs, liernes, tiercerons, etc., which appear in the later forms of vaulting,… are mere surface ribs having no real function.
1905. Bond, Goth. Archit., 74. Intermediate ribs, or tiercerons, were added in Lincoln nave.
