This etymology parses the word as a compound with the negation. In Late Greek that was pronounced [mi isos] because of iotacism, so that the assumption of a contraction between the negation and the initial vowel was easy. The interesting fact is that this explanation involves not the privative prefix, but the full negation μή, which is never used in compounds. Greek etymologists did nots see the difference between an autonomous negation and a non-autonomous one. As the autonomous negation can vary in scope, and apply either to the whole clause or to a word only, they considered it equivalent to the negative prefix, which applies to a word only (see also μήνη / μὴ μένειν, μῆνις / μὴ ἕν), on the model of μηδείς. The fact that μή is the prohibitive negation, which cannot be used in any context, was not taken into account