Green’s Dictionary of Slang

1. smartly dressed, dandified.

1860		Hotten Dict. of Modern Sl. etc.
1888		S.O. Addy Sheffield Gloss. 232: Spiff, fine, smart.
1896		G.F. Northall Warwickshire Word-Book 221: Spiff. [...] Fine, gay, first-rate, dapper.
1922		S. Lewis Babbitt (1974) 150: Spifly bonnets on their beans.

2. first-rate, excellent.

1866		Wild Boys of London I 83/2: ‘Shouldn’t like a gal to call me Sam; it’s wulgar.’ ‘What name would you like?’ ‘Something spiff.’.
1879		Sporting Times 1 Mar. 2/2: ‘It was a spiff affair, I can tell you. Right up to the knocker’.
1887		‘’Arry at the Sea-Side’ in Punch 10 Sept. 111/2: The larks on the sand, niggers, spotting the bathers, — that’s spiff!
1896		see sense 1.
1915		R. Bolwell ‘College Sl. Words And Phrases’ in DN IV:iii 235: spiff, adj. = spiffy.
1973		L. Bangs in Psychotic Reactions (1988) 116: There’s still an awful lot of spiff items that them damn channels ’ve got.
1999		Eble Campus Sl. Apr. 7: spif – cool, interesting: ‘That’s a spif costume.’.
2012		J. Fagan Panopticon (2013) 186: This is Anais Hendricks [...] to be me is really quite spiff-fucking-spuff.