- furtive, lurking, skulking, sneak, sneaky, stealthy, surreptitious - 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"
Antonym: unconcealed (indirect, via concealed)