Un`der*pin" (?), 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.
2.
To support by some solid foundation; to place something underneath for support.
© Webster 1913.