Centring, centre, centering, or center is a type of falsework: the temporary structure upon which the stones of an arch or vault are laid during construction. Once the arch is complete, it supports itself, but until the keystone is inserted, it has no strength and needs the centring to keep the voussoirs in their correct relative positions. A simp...
• (n.) See Centring. • of Centre
To position something in such a way that it is the same distance from all sides of an object: for example, centring copy or text on a plaque, or centring a name on a nameplate.
Temporary structure on which an arch is supported during construction, normally made from timbers.
Cen'tring noun See Centring . 
framing used to support an arch or dome while it is under construction.