waistyoudaoicibaDictYouDict
waist: [14] Waist is something of a mystery word, but it is generally taken to denote etymologically ‘girth to which one has grown’. It is probably descended from an unrecorded Old English *wæst, which would have gone back to prehistoric Germanic *wakhs- ‘grow’, source of English wax ‘grow’ (as in wax and wane). Related forms which support this hypothesis include Icelandic vöxstr and Gothic wahstus, which mean ‘growth, size’.
waist (n.)youdaoicibaDictYouDict
late 14c., "middle part of the body," also "part of a garment fitted for the waist, portion of a garment that covers the waist" (but, due to fashion styles, often above or below it), probably from Old English *wæst "growth," hence, "where the body grows," from Proto-Germanic *wahs-tu- (cognates: Old English wæstm, Old Norse vöxtr, 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- (1) "to increase" (see augment).