Green’s Dictionary of Slang

(esp. show business) wonderful, excellent.

1934		G. & S. Lorimer Stag Line 140: ‘Sock-o!’ Bill cried enthusiastically.
1939		W. Winchell On Broadway 19 June [synd. col.] Lou Holtz has given the Vallee folderol the sockoest wind-up its ever had.
1940		C. Rawson Headless Lady (1987) 38: The illusion is so perfect that it would still be a socko draw if it were announced as an illusion instead iof as the real thing.
1951		Green & Laurie Show Biz from Vaude to Video 5: Vaudeville, 1908–1913, was ‘socko’.
1958		Kerouac letter 16 Jan. in Charters II (1999) 109: Things looking up in movies, got big intellectual (classic) letter from big producer who wants big socko ending where Dean crashes and dies.
1966		H.S. Thompson Hell’s Angels (1967) 146: I didn’t mind and the deputy said it was a socko idea.
1983		(con. 1970) S. Wright Meditations in Green (1985) 333: Finish the picture [...] There’s no time for anything else, anyway Here, socko ending.
1994		K.M. Cameron Africa on Film 55: The loss in socko box-office was a gain in truth.
2004		D. Gomery Coming of Sound 59: The ‘boffo-socko’ blockbuster [...] that convinced all doubters was The Singing Fool.