Etymology
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*gno- 

*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."

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gnome (n.2)

"short, pithy statement of general truth," 1570s, from Greek gnōmē "judgment, opinion; maxim, the opinion of wise men," from PIE root *gno- "to know."

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astrognosy (n.)

"knowledge of the fixed stars, their names, magnitudes, etc.," 1835, from astro- "star" + -gnosy, from Greek gnōsis "a knowing, knowledge," from PIE root *gno- "to know."

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ken (n.1)
1550s, "cognizance, intellectual view;" 1580s in a physical sense, "range of sight;" from ken (v.), in the second sense perhaps via kenning (n.2) in the same sense in nautical use; both from PIE root *gno- "to know."
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gnosis (n.)

"knowledge," especially "special knowledge of spiritual mysteries," 1703, from Greek gnōsis "a knowing, knowledge; a judicial inquiry, investigation; a being known," in Christian writers, "higher knowledge of spiritual things," from PIE *gnō-ti-, from root *gno- "to know."

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anagnorisis (n.)
"recognition," especially in dramatic works, c. 1800, from Latin, from Greek anagnorisis "recognition," from anagnorizein "to recognize," from ana "again" (see ana-) + gnorizein "to make known, gain knowledge of," from PIE root *gno- "to know."
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chirognomy (n.)

"the supposed science of judging character from the lines and marks of the hand," 1868, from chiro- "hand" + -gnomy, from Greek gnome "judgment, opinion," from PIE root *gno- "to know." Related: Chirognomist.

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diagnosis (n.)

"scientific discrimination," especially in pathology, "the recognition of a disease from its symptoms," 1680s, medical Latin application of Greek diagnōsis "a discerning, distinguishing," from stem of diagignōskein "discern, distinguish," literally "to know thoroughly" or "know apart (from another)," from dia "between" (see dia-) + gignōskein "to learn, to come to know," from PIE root *gno- "to know."

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Zend (n.)
1715, "Parsee sacred book" (in full, Zend-Avesta, 1620s), from Old Persian zend, from Pahlavi zand "commentary," from Avestan zainti- "knowledge," from PIE root *gno- "to know." First used 1771 in reference to the language of the Zend-Avesta by French scholar Abraham Hyacinthe Anquetil-Duperron (1731-1805).
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notoriety (n.)

"state or character of being unfavorably known," 1590s, from French notoriété or directly from Medieval Latin notorietatem (nominative notorietas), from notorius "well-known," from Latin notus "known," past participle of noscere "come to know," from PIE root *gno- "to know." 

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