'Foolish' in the Bible

I am obligated both to Greeks and barbarians, both to the wise and the foolish.

Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.

Seeming to be wise, they were in fact foolish,

foolish, faithless, heartless, and ruthless.

An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law.

But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.