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’.
