Why is the ninth month called September?
before vowels meg-, word-forming element often meaning "large, great," but in precise scientific language "one million" (megaton, megawatt, etc.), from Greek megas "great, large, vast, big, high, tall; mighty, important" (fem. megale), from PIE *meg- "great" (cf. Latin magnus, Old English micel; see mickle). Mega began to be used alone as an adjective by 1982.
High-speed computer stores 2.5 megabits [headline in "Electronics" magazine, Oct. 1, 1957]
One million (106): megahertz.
Much: I got mega homework tonightadverb
Very: This dude is mega gross (1980s+ Students & teenagers)
A very large specimen, quantity, etc, of what is indicated: megabitch/ megablitz/ mega-cost/ megafame/ megagreed/ megahopes/ megamodel/ mega-travel (1981+)