A [lisp](http://oxforddictionaries.com/definition/english/lisp) is a "a speech defect in which ***s* is pronounced like *th*** in thick and z is pronounced like th in this". Its etymology reads:

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> Old English wlispian (recorded in āwlyspian), from wlisp (adjective) 'lisping', **of imitative origin**; compare with Dutch lispen and German lispeln
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What does *imitative* mean here? Onomatopoeic? Considering the word's definition, how is that even possible?

It seems like a rather cruel etymological in-joke.