Definition of "scullduggery"

[…] I discovered this particular one to be merely a shallow recess in the limestone, nowhere reëntrant to a distance of over forty feet, of the general proportions of a tin oven, and transacting an immense business of mystery (or what they call, as far west as this, "Shenandigan" and "Scullduggery") with those who gape at it from below, on the capital of a dark, overgrown portal, as big as the cave itself.

1870, Fitz Hugh Ludlow, “The Dead Sea.—The Physical Geography and History of Its Basin.”, in The Heart of the Continent: A Record of Travel across the Plains and in Oregon, with an Examination of the Mormon Principle, New York, N.Y.: Published by Hurd and Houghton […], page 385

Reverting to the Lübeck plan, one need perhaps shed no tears for the KGB, and the GRU (the Soviet CIA), deprived of their preferred choice as a scullduggery base of Kiel, where the Federal German navy has an installation.

1985, Fairplay, volume 293, London: IHS Markit, page 151, column 1