1. 
[syn: backstair, backstairs, furtive]
The Collaborative International Dictionary of English v.0.48:
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]
WordNet (r) 3.0 (2006):
backstair
    adj 1: secret and sly or sordid; "backstairs gossip"; "his low
           backstairs cunning"- A.L.Guerard; "backstairs
           intimacies"; "furtive behavior" [syn: backstair,
           backstairs, furtive]