ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ ̷ ̷ noun
Etymology: under (III) + pinning
1.
a. : the material and construction used for support and introduced beneath a wall already constructed
b. : the foundation of a frame house
2. : a method of lining a mine shaft by supporting the upper section of brickwork on a curb by shores or props, excavating below, and building up to this curb from another curb inserted lower down
3. : support , prop
military security depends on a strong economic underpinning — H.S.Truman
4. : underwear — used usually in plural
5. : a person's legs — used usually in plural
still unsteady on his underpinnings when he came out for the seventh — Ring