Hidden, out of sight or inconspicuous.
Dark, faint or indistinct.
Difficult to understand.
Not well-known.
Unknown or uncertain; unclear.
To hide, put out of sight etc.
To render obscure; to darken; to make dim; to keep in the dark; to hide; to make less visible, intelligible, legible, glorious, beautiful, or illustrious.
That cannot be investigated or searched into; unknowable, inscrutable.
Not capable of being searched; on which one cannot perform a search.
That cannot be sought out or looked for.