Agnostic - A person who believes that, at our present level of knowledge, we cannot know whether or not a God exists. Some Agnostics believe that we can never know whether a deity exists.

Agnosticism is the philosophical view that the truth values of certain claims, particularly theological claims regarding the existence of God, gods or deities, are either unknown or inherently unknowable. The term and the related agnostic were coined by Thomas Henry Huxley in 1869 and are also used to describe those who are unconvinced or noncommittal about the existence of deities as well as other matters of religion. (wikipedia)

An Agnostic [1] [noun] [OW] embraces a worldview in which the existence of deity is unknown or unknowable. Derives from the Greek agnostos, a = without, gnostos = known or knowledge. "Agnostic[ism] [CE] was coined by Professor TH Huxley in 1869 to describe the mental attitude of one who regarded as futile all attempts to know the reality corresponding to our ultimate scientific, philosophic, and religious ideas." (AOL)

Agnostic one who believes that the evidence for and against the existence of God is inconclusive. (summit)