Obscure, mysterious.
Understood by only a few.
Extremely old (e.g. interpretation or knowledge), and possibly irrelevant.
Requiring secret or mysterious knowledge to understand.
Uncertain, as an indication or sign.
Having two or more equally applicable meanings; capable of double or multiple interpretation.
Capable of being ascribed to different motives, or of signifying opposite feelings, purposes, or characters; deserving to be suspected.
A word or expression capable of different meanings; an ambiguous term.