/un"deuhr pin'ing/ , n.
1. a system of supports beneath a wall or the like.
2. Often, underpinnings . a foundation or basis: to uncover the emotional underpinnings of an illness.
3. underpinnings , Informal.
a. underwear, esp. women's underwear.
b. the legs.
[ 1480-90; UNDER + PIN + -ING 1 ]