The word is defined on the basis of its Middle English gloss. It is not attested anywhere else and its etymology remains unidentified.
s.
1archit.groundsel, sill, large beam or piece of timber that supports a superstructure or serves as a foundation:
(
s.xivin; MS: 1382
) Clowes, kyvyls et guenchons (M.E. Nayles, pynnes and lathes), Traches et trenchons (M.E. Sulle-trees and splentes) Et meynte autre gobons Piler desouz le poutre
448
trache1 (s.xivin)