centring
(ˈsɛntrɪŋ) or centering
n (Building) a temporary structure, esp one made of timber, used to support an arch during construction
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014