unviewable

imperceptible microscopic unseen

inconspicuous unseeable

concealed covert deceptive disguised ethereal gaseous ghostly ideal impalpable imponderable inappreciable indiscernible infinitesimal insensible intangible masked not in sight obliterated obscured occult out of sight perdu screened supernatural ulterior unapparent undisclosed ungraspable unnoticeable unobservable unperceivable unreal vaporous veiled wraithlike

detectable obvious seen visible