Definitions for "Tierceron"
Keywords:  vault, rib, ridge, martindale, lierne
In vault construction, a secondary rib that arcs from a springing point to the rib that runs lengthwise through the vault, called the ridge rib.
A rib that is neither a transverse nor a diagonal rib but which springs from the same point and reaches to the crown of the vault. (Martindale, Andrew. Gothic Art, 269)
Additional major rib that springs from the supporting pier and rises to meet the ridge rib over the nave or in the window bay.