ivver

This is the ordinary Hebrew word for a blind person, and most of the time it means exactly what it says: someone (or, in the sacrifice laws, an animal) whose eyes do not work. The Law protects such people and treats their condition as a real, God-given hardship, and the prophets promise a day when the blind will see again.

From that plain meaning the word stretches, as the English word blind does, to describe people whose eyes work perfectly well but who still cannot perceive what is in front of them. This figurative use clusters in the second half of Isaiah, where God calls his own servant and people blind: they have eyes, yet they do not grasp what God is doing. The same picture of blindness stands for helplessness elsewhere, where people stagger and grope as though they could not see.

Both uses share one core idea, the inability to see, so they are one word with two shades rather than two different words. The line between them is drawn by context, and a few verses can be read either way.