D defs.my
Entry 2 senses Webster, 1913

Underpin

/ŭn'-dẽrp-ĭnˌ/ · Un·der·pin · IPA /ˌʌn.dɚˈpɪn/
01 v. t. To lay stones, masonry, etc., under, as the sills of a building, on which it is to rest.
imp. & p. p. Underpinned; p. pr. & vb. n. Underpinning
  1. 1.
    To lay stones, masonry, etc., under, as the sills of a building, on which it is to rest.
  2. 2.
    To support by some solid foundation; to place something underneath for support.