Etymology
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incognito (adj./adv.)
1640s as both adjective ("disguised under an assumed name and character") and adverb ("unknown, with concealed identity"), from Italian incognito "unknown," especially in connection with traveling, from Latin incognitus "unknown, not investigated," from in- "not, opposite of, without" (see in- (1)) + cognitus, past participle of cognoscere "to get to know" (see cognizance). Also as a noun, "an unknown man" (1630s). Feminine form incognita was maintained through 19c. by those scrupulous about Latin. Incog was a common 18c. colloquial abbreviation.
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terra incognita (n.)
"unknown or unexplored region," 1610s, Latin, literally "unknown land," from terra "earth" (from PIE root *ters- "to dry") + fem. of incognito.
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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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