"relating to knowledge," especially mystical or esoteric knowledge of spiritual things, 1650s, from Greek gnōstikos "knowing, good at knowing, able to discern," from gnōstos "known, perceived, understood," earlier gnōtos, from gignōskein "learn to know, come to know, perceive; discern, distinguish; observe, form a judgment," from PIE *gi-gno-sko-, reduplicated and suffixed form of root *gno- "to know."
1580s, "believer in a mystical religious doctrine of spiritual knowledge," from Late Latin Gnosticus "a Gnostic," from Late Greek Gnōstikos, noun use of adjective gnōstikos "knowing, able to discern, good at knowing," from gnōstos "known, to be known," from gignōskein "to learn, to come to know," from PIE root *gno- "to know." Applied to various early Christian sects that claimed direct personal knowledge beyond the Gospel or the Church hierarchy; they appeared in the first century A.D., flourished in the second, and were stamped out by the 6th.
*gnō-, Proto-Indo-European root meaning "to know."
It forms all or part of: acknowledge; acquaint; agnostic; anagnorisis; astrognosy; can (v.1) "have power to, be able;" cognition; cognizance; con (n.2) "study;" connoisseur; could; couth; cunning; diagnosis; ennoble; gnome; (n.2) "short, pithy statement of general truth;" gnomic; gnomon; gnosis; gnostic; Gnostic; ignoble; ignorant; ignore; incognito; ken (n.1) "cognizance, intellectual view;" kenning; kith; know; knowledge; narrate; narration; nobility; noble; notice; notify; notion; notorious; physiognomy; prognosis; quaint; recognize; reconnaissance; reconnoiter; uncouth; Zend.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit jna- "know;" Avestan zainti- "knowledge," Old Persian xšnasatiy "he shall know;" Old Church Slavonic znati "recognizes," Russian znat "to know;" Latin gnoscere "get to know," nobilis "known, famous, noble;" Greek gignōskein "to know," gnōtos "known," gnōsis "knowledge, inquiry;" Old Irish gnath "known;" German kennen "to know," Gothic kannjan "to make known."
1870, "one who professes that the existence of a First Cause and the essential nature of things are not and cannot be known" [Klein]; coined by T.H. Huxley, supposedly in September 1869, from Greek agnostos "unknown, unknowable," from a- "not" (see a- (3)) + gnōstos "(to be) known," from PIE root *gno- "to know." Sometimes said to be a reference to Paul's mention of the altar to "the Unknown God" in Acts, but according to Huxley it was coined with reference to the early Church movement known as Gnosticism (see Gnostic). The adjective also is first recorded 1870.
I ... invented what I conceived to be the appropriate title of 'agnostic,' ... antithetic to the 'Gnostic' of Church history who professed to know so much about the very things of which I was ignorant. [T.H. Huxley, "Science and Christian Tradition," 1889]
The agnostic does not simply say, "I do not know." He goes another step, and he says, with great emphasis, that you do not know. [Robert G. Ingersoll, "Reply to Dr. Lyman Abbott," 1890]
Cabalistic word associated with the followers of Basilides the Gnostic, by 1680s, of uncertain origin and with many elaborate explanations. Also used in reference to a type of Gnostic amulet featuring a carved gem depicting a monstrous figure and obscure words or words connected to Hebrew or Egyptian religion (1725).
mid-15c. in reference to a Christian heresy that took root in 4c. Spain, from Priscillian, bishop of Ávila, whose followers held ascetic and Gnostic doctrines. For the name, see Priscilla. Also a name given to 2c. Montanists, from their prophetess Prisca or Priscilla.