Definition of "topping"

“My boy came home last night,” sang the waitress. “Oh, I say–how topping for you !” gurgled the cashier.

1919, Katherine Mansfield [pseudonym; Kathleen Mansfield Murry], “Pictures”, in Bliss and Other Stories, London: Constable & Company, published 1920, page 162

'Well,' he said, settling back in the seat directly opposite. 'It's a topping day.'

1953, Roald Dahl, Galloping Foxley

A second Ground, upon which Men are apt to persuade themselves, that they shall escape the Stroke of Divine Justice for their Sins, is their Observation of the great and flourishing Condition of some of the topping Sinners of the World.

1692–1717, Robert South, Twelve Sermons Preached upon Several Occasions, 6th edition, volumes (please specify |volume=I to VI), London: […] J[ames] Bettenham, for Jonah Bowyer, […], published 1727