[bæk'steә(r)]
adj.
间接的

[ adj ]
secret and sly or sordid
<adj.all>
backstairs gossiphis low backstairs cunning
backstairs intimacies
furtive behavior

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.

Female caprice and backstair influence.
--Trevelyan.