From WordNet (r) 2.0 (August 2003) [wn]:
backstair
adj : secret and sly or sordid; "backstairs gossip"; "his low
backstairs cunning"- A.L.Guerard; "backstairs
intimacies"; "furtive behavior" [syn: backstairs,
furtive]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Backstairs \Back"stairs`\, Backstair \Back"stair`\, a.
Private; indirect; secret; conducted with secrecy;
intriguing; -- as if finding access by the back stairs; as,
backstairs gossip.
Syn: clandestine, cloak-and-dagger, hugger-mugger, hush-hush,
on the quiet(predicate), secret, subterranean,
surreptitious, undercover, underground.
[1913 Webster + WordNet 1.5]
A backstairs influence. --Burke.
[1913 Webster]
Female caprice and backstair influence.
--Trevelyan.
[1913 Webster]