Green’s Dictionary of Slang

smacking adj.

good, excellent.

1735		Pope ‘Epistle VI’ Works II 76: Then gives a smacking buss, and cries, – No words!
1821–6		‘Bill Truck’ Man o’ War’s Man (1843) 41: Here’s smacking luck to you, my dear boy.
1936		J.T. Farrell World I Never Made 502: She gave him a smacking kiss on the cheek.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 181: Other superlatives in favour were: [...] smacking, smasho, super.

In derivatives

smackingly (adv.)

smartly, speedily.

1843

Fife Herald 29 June 16/1: So away to wet Tibur [...] The threesome went smackingly by.