Unclear:
* Ambiguous: Open to more than one interpretation; unclear.
* Obscure: Not easily understood or seen; unclear.
* Indistinct: Not clear or sharply defined; vague.
* Fuzzy: Not clear or precise; vague.
* Nebulous: Hazy, unclear, or ill-defined.
* Opaque: Not transparent; difficult to understand.
Vague:
* Imprecise: Not exact or specific; vague.
* Indeterminate: Not fixed or definite; unclear.
* General: Not specific or detailed; broad.
* Abstract: Existing in thought or as an idea but not having a physical or concrete existence; vague.
Hidden:
* Concealed: Kept secret or hidden from view.
* Disguised: Made to look different from what it really is; hidden.
* Latent: Present but not yet active or developed; hidden.
* Covert: Secret or hidden; clandestine.
* Subterranean: Existing or occurring below the surface of the earth; hidden.
The best word to use will depend on the specific context and the nuance you want to convey.