waist (n.) Look up waist at Dictionary.com
"middle part of the body," also "part of a garment fitted for the waist," late 14c., probably from Old English *wæst "growth," hence, "where the body grows," from Proto-Germanic *wahs-tu- (cf. Old English wæstm, Old Norse vaxtr, Swedish växt, Old High German wahst "growth, increase," Gothic wahstus "stature," Old English weaxan "to grow" see wax (v.)), from PIE *wegs-, extended form of root *aug- "to increase" (see augment). Meaning "portion of a garment that covers the waist" (but, due to fashion styles, often is above or below it) is from 1640s.