Definition of "naïf"

Doenitz was naïf to assume that England would have stood idly by while Germany built up her U-boat force to four figures; but it was true enough that the German Navy was unprepared for a submarine war.

1947, S.E. Morison, History of United States Naval Operations in World War II, Little, Brown, & Company, page 5

Now I could see there was no real rogue here, but a naïf who thought that world would always turn for him.

2008, Monte Dwyer, Red In The Centre: The Australian Bush Through Urban Eyes, Monyer Pty Ltd, page 145

On “Fearless,” Swift sharpened her lyrical specificity, using proper nouns and detailed renderings of conversations and experiences to create an indelible image of Taylor Swift, the savvy naïf.

2021 April 12, Carrie Battan, “Taylor Swift Wins with “Fearless (Taylor’s Version)””, in The New Yorker‎