Green’s Dictionary of Slang

elegant, fashionable, distinguished.

1834		(con. 1737–9) W.H. Ainsworth Rookwood (1857) 178: All my togs were so niblike and splash.
1931		W.N. Burns One-Way Ride 35: Cracksmen assembled to blow a safe had the appearance of dandies gathered for wafers and tea at some function of splash society.