marked by quiet and caution and secrecy; taking pains to avoid being observed; "a furtive manner"; "a lurking prowler"; "a sneak attack"; "stealthy footsteps"; "a surreptitious glance at his watch"; "someone skulking in the shadows"
disapproval If you describe someone as sneaky, you disapprove of them because they do things secretly rather than openly. It is a sneaky and underhand way of doing business = sly. doing things in a secret and often dishonest or unfair way