Dr. P.A.F. van Veen e.a., Etymologisch Woordenboek. De herkomst van onze woorden., Van Dale Lexicografie, 1989 [Dutch etymological dictionary, in Dutch]
Etymology
the root of kletsen 'to chatter' + kous 'stocking' (the second component is popular etymology for a variant on kouten 'to babble')