Root? From the French "inconnaitre"?

From the French "inconnaitre"?

Yes, it means unknown in English. It's a past participle. From the Latin incognitus < in- 'not, un-' + cognosco 'to know'. It's related to the name of a fictionarl character in Middle English literature: Libeaus Desconus < Anglo-Norman li bel inconnu 'the fair unknown'.