AbstractDespite the numerous attempts at clarification that have been made over the past hundred years or so, there are still many doubts surrounding the etymology of Gr. μέγας, μεγάλη, μέγα “big, great, mighty”, especially with regard to the relation between the Greek adjective and forms attested in other Indo-European languages. The paper follows a new track. By having recourse to É. Benveniste’s theory of the structure of the Indo-European root, a stem II *sm-eĝ- is supposed in which *s- could share the characteristics of the so-called ‘mobile s-’. Thanks to this hypothesis most of the pre-existing doubts are dispelled.