agnostic

(noun) someone who is doubtful or noncommittal about something. Synonyms: doubter.

(noun) a person who claims that they cannot have true knowledge about the existence of God (but does not deny that God might exist).

(adj) of or pertaining to an agnostic or agnosticism.

(adj) uncertain of all claims to knowledge. Synonyms: agnostic (vs. gnostic), agnostical.