Meaning

noun someone who is doubtful or noncommittal about something

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

adjective of or pertaining to an agnostic or agnosticism

originCoined by Thomas Henry Huxley in 1870. Either from Ancient Greek ἄγνωστος (ágnōstos, “ignorant, not knowing”), or from a- + Gnostic, deriving (either way) from Ancient Greek ἀ- (a-, “not”) + γιγνώσκω (gignṓskō, “I know”).

Etymology from Wiktionary, CC BY-SA 3.0