behind the curtain, behind the scenes, concealed, disguised, hidden, imperceptible, in disguise, incog, incognito, indiscernible, insensible, invisible, latent, masked, masquerading, out of sight, secret, sightless, submerged, unapparent, unbeheld, unbeholdable, undiscernible, unnoticed, unobserved, unperceivable, unperceived, unrealized, unseeable, unseen, unviewed, unwitnessed, viewless