naïf

/na.if/
1.
adjectivemasculine

naive; lacking experience, sophistication or worldly knowledge

gullible; inclined to believe things too readily

T'es vraiment naïf de croire tout ce qu'il te dit.

You're really naive to believe everything he tells you.

2.
nounmasculine

a naive person; someone gullible or easily deceived

Ne fais pas le naïf avec moi, je sais que tu savais.

Don't play the innocent with me, I know you knew.