Select the word which means the same as the group of words given. That which is incapable of being read or understood

Indelible Illegible Illegal Intelligible

Illegible

The word that means the same as the group of words "that which is incapable of being read or understood" is illegible. Indelible means impossible to remove or wash out. Illegal means not allowed by the law. Intelligible means possible or easy to understand.