desconocido
/deskonoˈθido/ · B1 · adj
unknown, undisclosed, unbeknownst
🗺️❓ des- (un-) + conocido (known) = un-known; conocer shares a root with cognition
conocer comes from Latin cognoscere, to get to know, the same root as English cognition and recognise. Add the negating prefix des- and the -ido past participle ending, and you get not-known: desconocido.