Underpinning

n.	1.	The act of one who underpins; the act of supporting by stones, masonry, or the like.
	2.	(Arch.) That by which a building is underpinned; the material and construction used for support, introduced beneath a wall already constructed.

base, basement, basis, bearing wall, bed, bedding, bedrock, brace, buttress, column, floor, flooring, fond, footing, foundation, fundament, fundamental, ground, grounds, groundwork, hardpan, infrastructure, pavement, principle, prop, radical, riprap, rock bottom, root, rudiment, seat, seating, shore, sill, solid ground, solid rock, stay, stereobate, stylobate, substratum, substruction, substructure, terra firma, underbuilding, undercarriage, undergirding, understruction, understructure