Definition of "backstairs"

Here I diſcovered the ſecret Cauſes of many great Events that have ſurprized the World, how a Whore can govern the Back-ſtairs, the Back-ſtairs a Council, and the Council a Senate.

1726 October 28, [Jonathan Swift], “A Further Account of Glubbdubdrib. […]”, in Travels into Several Remote Nations of the World. […] [Gulliver’s Travels], volume II, London: […] Benj[amin] Motte, […], part III (A Voyage to Laputa, Balnibarbi, Glubbdubdribb, Luggnagg, and Japan), page 111

Other feet were already in the lower flight of the backstairs; but the upper flight was the one for me, and in an instant we were racing along the upper corridor […]

1905, Ernest William Hornung, “The Spoils of Sacrilege” in A Thief in the Night

The straight-forward course, they say, would be to proclaim outright, instead of trying to bring it in by the backstairs.

1934 March 27, “De Valera Move Hits Dignity Of Governor-General”, in Christian Science Monitor

[…] if some peers (I am very sorry they are not as many as they ought to be) set themselves, in the great concern of peers and commons, against a back-stairs influence and clandestine government, then the alarm begins; then the constitution is in danger of being forced into an aristocracy.

1770, Edmund Burke, Thoughts on the Cause of the Present Discontents‎

The danger of the situation was increased by the mischievous conduct of Alderman Townshend, who had been brought down to the House, pale and bandaged from a recent surgical operation, in order to pour forth a diatribe against female caprice and backstairs influence; […]

1880, George Otto Trevelyan, chapter 8, in The Early History of Charles James Fox‎, London: Longmans, Green, and Co., published 1881, page 364

This backstairs visit was all about sex […]

2004, Alan Hollinghurst, chapter 3, in The Line of Beauty […], 1st US edition, New York, N.Y.: Bloomsbury Publishing