adjective

attempting to avoid notice or attention, typically because of guilt or a belief that discovery would lead to trouble; secretive.

they spent a furtive day together

secretive,secret,surreptitious,sly,sneaky,wily,underhand,under the table,clandestine,hidden,covert,cloaked,conspiratorial,underground,cloak and dagger,hole and corner,hugger-mugger,stealthy,sneaking,skulking,slinking,sidelong,sideways,oblique,indirect,black,hush-hush,shifty