furtive

marked by quiet and caution and secrecy; taking pains to avoid being observed; "a furtive manner"; "a sneak attack"; "stealthy footsteps"; "a surreptitious glance at his watch"

secret and sly or sordid; "backstairs gossip"; "his low backstairs cunning"- A.L.Guerard; "backstairs intimacies"; "furtive behavior"