Green’s Dictionary of Slang

1. of an object or person, superlative, excellent, extra-special; usu. as pfx.

1966		Current Sl. I:3 5/2: Mega, adv. The ultimate.
1984		C. White Life and Times of Little Richard 56: I could tell he was a mega-personality.
1991		M. Myers et al. Wayne’s World [film script] This band ‘Crucial Taunt,’ had this megababe for a lead singer.
1999		K. Sampson Powder 192: Tomorrow is such a mega important day.
2001		‘John le Carré’ Constant Gardener 275: I’ve landed myself with a five-star mega-creep with the hots for me.
2012		D. Spivey ‘If You Were Only White’ 89: The auditions culminated with a mega performance in Soldier Field.

2. of an object, huge, enormous, substantial.

1942		P. Wylie Generation of Vipers 185: Megaloid momworship has got completely out of hand.
1967–8		Baker et al. CUSS 156: Mega load A great deal of something.
1968		Harper’s Mag. Feb. 61: The noisy, ugly, chaotic, increasingly dangerous and ever-spreading mega-cities.
1970		Times 27 June 13: The closer links which are already developing within the personal finance industry, could be logically developed into a mega-association for all parties.
1981		Eble Campus Sl. Mar. 4: mega – large quantity.
1986		Newcastle Eve. Chronicle 29 Aug. 10: It’s a perfect mega-read for the beach, guaranteed to keep you happy for the whole fortnight.
1990		S. Morgan Homeboy 4: Taking a megachomp out of a weenie.
1997		N. Barlay Curvy Lovebox 12: The bitch blows a mega raspberry.
1998		A. Warner Sopranos 308: The mega-rich guy went bust!
2000		Guardian G2 24 Jan. 3: JK Rowling’s mega-selling Harry Potter.
2002		S. Maloney Something Fishy (2006) 75: He goes to work, never comes home. Vanishes. So does mega-tits, his bit on the side.
2007		Courier-Post (Camden, NJ) 25 Sept. 53/1: Mega-bombs [...] [TV] shows I enjoyed but which [...] can only be described as stinkeroos .
2017		News Jrnl (Wilmington DE) 4 Oct. D3/1: The mega-sized eclairs have proven to be a hit.

3. of a person, very well known or very successful, also later used predicatively e.g. the movie was mega.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 10: He had read in the Johnny Raper that Balmain had been taken over by the mega-trendies and the would-be-if-they-could-be brigades.
1996		J. Cameron It Was An Accident 193: Reckoned it was some film script maybe. I was mega round there.

4. of a person, extreme in type.

1985

in Tracks (Aus.) Aug. 5: Semi-yobbs, mega-yobbs, yobettes.