Green’s Dictionary of Slang

1. (also big dealer) an important (or self-important) person.

1947		D.W. Hamilton ‘Pacific War Lang.’ in AS XXII:1 Feb. 54: big deal, A BTO, a big shot.
1947		B. Schulberg Harder They Fall (1971) 256: Dis guy’s a big dealer [...] He’s got a car, it looks like they put wheels on a speed-boat.
c.1960		Wilson Collection n.p.: big dealer [...] name for self-important person [DARE].
1963		in T.I. Rubin Sweet Daddy 32: Let him go to one of these big deals.
1970		in DARE.
1979		E. Torres After Hours 170: Macho [...] told Gail what a big deal I was.
1988		(con. 1940s) C. Bram Hold Tight (1990) 68: I don’t know who, but some big deal’s got his finger in this pie.
1990		M. McAlary Crack War (1991) 14: His father, Matt Byrne, had been a big deal on the job [...] He knew police chiefs, prosecutors, and judges.
2006		D. Winslow Winter of Frankie Machine (2007) 62: Momo was a big deal in San Diego, but everyone knew that San Diego was really run from L.A.
2015		S. King Finders Keepers (2016) 95: To the provincials, John was a big deal.
2015		N. Cummins Tales of the Honey Badger [ebook] We jumped ther queue — one of the perks of being a ‘big deal’.
2020		D. Winslow ‘Sunset’ in Broken 190: Neal is [...] a big deal in his field.

2. (also deal) anything that is considered important to the speaker; often ironic.

1923		Boys’ Life Oct. 9/1: ‘This is a big deal, Langdon, big deal.’ ‘Yeah?’ Langdon looked up intently. ‘Biggest cargo of the year, Langdon’.
1944		P. Kendall Dict. Service Sl. n.p.: big deal . . . uncalled for action.
1949		N. Algren Man with the Golden Arm 109: You’d think it was a big deal, tryin’ to make a chick.
1951		J.D. Salinger Catcher in the Rye (1958) 132: What a deal that was. You never saw so many phonies in all your life.
1955		B. Schulberg On the Waterfront (1964) 239: Do you have to make such a big deal out of it?
1962		R. Cook Crust on its Uppers 47: Big deal. Really big.
1975		E. Torres Carlito’s Way 10: The good girls held on to their cherry. And it was a big deal.
1982		G.V. Higgins Patriot Game (1985) 5: She got all mad again and came in and started reading out Mrs. Tobin and Bishop Doherty told her to shut up, there was no need to make a big deal out a small matter.
1999		Guardian Media 2 Aug. 3: You have to remember that LSD was a very big deal.
2000		Sun. Times News Rev. 12 Mar. 1: It’s no big deal to me to have a house in Westminster.
2005		L. Theroux Call of the Weird (2006) 130: Is that such a big deal, having sex in the negotiating room?
2014		E. Pruitt ‘Houston’ in ThugLit Mar. [ebook] [I]t wasn't a big fucking deal that he just let thirty-four hundred dollars disappear.
2017		G. Gilmore Headland [ebook] ‘It’s no big deal’.
2020		A. Parks Bobby March Will Live Forever 39: If McCoy needed reminding what a big deal the Glasgow Fair was, he got it as soon as the cab turned into Killermont Street.
2021		P. Papathanasiou Stoning 115: ‘Am I the only one who thinks that’s a big deal?’.