Green’s Dictionary of Slang

very, exceedingly; thus (brand) spanking new.

1850		Fast Man 13:1 n.p.: With a girl on each arm and a glass in my eye, / An opera hat, and a spanking great tie. / I’m a rake.
1901		Sydney Sportsman (Surry Hills, NSW) 21 Aug. 1/5: There you’ll see them spankin’ neat, / Bookies with their well-cut togs on.
1902		J. Masefield ‘A Valediction’ in Salt-Water Ballads 37: Well, so-long, Billy, ’n’ a spankin’ heavy pay-day to you!
1905		J.W. Carr ‘Words from Northwest Arkansas’ in DN III:i 71: bran spankin’ new, adj. Absolutely new.
1910		Bulletin (Sydney) 25 Aug. 40/3: ‘My oath, you must ’a’ spent money like water – two spankin’ good soots!’ cried Jim. / ‘Well, you can’t wear dungarees in an office.’.
1943		R. Llewellyn None But the Lonely Heart 281: Me and Taz got a pram [...] It’s one of them big new Yanks. Smashing job it is. Brand spanking new.
1966		Kerouac letter 18 Dec. in Charters II (1999) 431: We’re going to have a lot of fun in our spanking (practically) new house.
1970		T. Southern Blue Movie (1974) 185: A spanking new ‘orgy version’ of the so-called Around the Clock number.
1979		‘Iceberg Slim’ Airtight Willie and Me 133: He [...] got into his spanking new 1938 white Caddie.
1999		Indep. Rev. 27 July 9: Lehnhoff’s spanking new production.
1999		Indep. on Sun. Real Life 10 Oct. 8: Your leathers have to look brand spanking new.
2000		Guardian Rev. 29 Jan. 4: A spanking new C90 and an ample record collection.
2005		J. Stahl I, Fatty 91: A spanking-new coupe.