covert

abstruse behind the scenes backroom catlike stealth clandestine cloak-and-dagger concealed confidential deep-laid dern disguised furtive huggermugger hush-hush inconspicuous incognito low profile lurksome lurky mousy obfuscated on the down-low off-the-books on the sly secret secretive slinky sly sneaky stealthy sub rosa surreptitious under-the-table under the radar undercover under wraps underground unperceived