v. t. [ imp. & p. p. Underpinned p. pr. & vb. n. Underpinning. ] 1. To lay stones, masonry, etc., under, as the sills of a building, on which it is to rest. [ 1913 Webster ]

2. To support by some solid foundation; to place something underneath for support. [ 1913 Webster ]

n. 1. The act of one who underpins; the act of supporting by stones, masonry, or the like. [ 1913 Webster ]

2. (Arch.) (a) That by which a building is underpinned; the material and construction used for support, introduced beneath a wall already constructed. (b) The foundation, esp. of a frame house. [ Local, U. S. ] [ 1913 Webster ]