Commentary Par XXII 132

The word etera, literally translated, means '(a)ether,' in Aristotle's sense of the 'fifth element,' as understood by Jacopo della Lana (DDP Lana.Par.XXII.130-132), that which composes the 'stuff' of which a celestial sphere consists and in which other bodies (e.g., the stars) are contained.  It is thus differentiated from both stars (and what we refer to as planets) and nothingness (what we used to refer to as 'space').