somebody who holds the view that any ultimate reality is unknown and prob unknowable
somebody who believes that it is impossible to know whether God or any other supreme being exists or not
An agnostic holds the view that beliefs should be accepted on the basis of reason and evidence, and that there is insufficient evidence to justify belief in the existence of God. This does not imply that there is no God, but that his existence cannot be known. It is also taken generally to refer to a critical and sceptical view of religious belief — Dr Mel Thompson
somebody who is doubtful or non-committal on a particular question
agnostic adj
agnosticism /-stisizəm/ noun
modification of Greek agnōstos unknown, unknowable, from a-2 + gnōstos known, from gignōskein to know. The word was created in 1869 as an antonym of gnostic by the biologist Thomas Henry Huxley, who felt the need of a label for his own philosophical viewpoint