Derivational etymology, reversing the real linguistic relationship. Ἡλίθιος is assumed to be derived from its denominative ἠλιθιάζω. This etymology was probably designed to provide a better explanation for the assumed relationship between ἠλίθιος and λίθος (see ἠλίθιος / λίθος). By assuming that λίθος is not directly the etymon of ἠλίθιος, but that of ἠλιθιάζω, which is itself the etymon of ἠλίθιος, the semantic derivation is less awkward: "stone" → "to be insensitive and stupid as a stone" → "fool, stupid"