Obscure, mysterious.
Understood by only a few.
Extremely old (e.g. interpretation or knowledge), and possibly irrelevant.
Requiring secret or mysterious knowledge to understand.
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.