Greek ακνηστις aknēstis 'backbone' < κνηστις knēstis 'spine; cheesegrater' < PIE *kenə-, knē- 'to scratch, scrape, rub'. The words are quite rare and their meanings did not seem to stop Homer from using them: the former in Odyssey 10.161 (a stag is struck by Odysseus' bronze spear in the spine) and the latter in Iliad 11.640 (a bronze grater is used to grate cheese into a cup of wine). It does not seem like to far a semantic journey from a cheese grater to a spine.

Ceci n'est pas un seing.