Green’s Dictionary of Slang

very; often as socking great, very great, enormous.

1896		DN I 425: That was a socking big fish.
1901		Monroe & Northup ‘College Words and Phrases’ in DN II:iii 148: socking, adv. Very; ‘socking good’.
1903		Monroe City Democrat (MO) 22 Oct. 3/4: B’ar arter the pig! [...] A sockin’ big ba’r.
1940		J. MacLaren-Ross ‘A Bit of a Smash in Madras’ in Memoirs of the Forties (1984) 273: I kept drinking socking great cups of black tea.
1945		P. Larkin letter 9 Aug. in Thwaite Sel. Letters (1992) 104: Your socking great letter arrived this morning most opportunely on my birthday.
1959		H. Ellison ‘This Is Jackie Spinning’ in Gentleman Junkie (1961) 71: Her rocking, socking version of that big sensation.
1988		T. Jones Curse of the Vampire Socks 112: There they both live, / With a socking great car.
1995		D. Lodge Therapy (1996) 100: A socking great book, in two volumes.
2000		Indep. Rev. 4 Apr. 7: Sainsbury’s is one socking great advertisement for Christianity.