D defs.my
Entry 2 senses Webster, 1913

Underpinning

/ŭn'-dẽrp-ĭnˌ-ĭng/ · Un·der·pin·ning · IPA /ˈʌndərpˌɪnɪŋ/
01 n. The act of one who underpins; the act of supporting by stones, masonry, or the like.
  1. 1.
    The act of one who underpins; the act of supporting by stones, masonry, or the like.
  2. 2.
    That by which a building is underpinned; the material and construction used for support, introduced beneath a wall already constructed.(Arch.) [Local, U. S.]