Synonyms and related words :
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