Entry record from de Josselin de Jong (1947): Ili'uun Erai
mega
• an adverbial particle of manifold use, whose primary sense it is difficult to determine at present; it is often used with the meaning of "then", referring to what follows next, or of "already", referring to what has happened or has been done..
Note: In many cases its general function is to express emphasis, and it may be translated in different ways according to the situation, as: just, only, any more, altogether, perhaps, rather.