If a person or an animal is ineducable, you cannot teach them, or it is extremely hard to teach them — they do not take in lessons, training, or new habits. This is a strong, rather formal word. You meet it in older writing about schools, and sometimes in talk about a child or student who seems to learn almost nothing, no matter what you try. It can sound cold, even unkind, if you say it about a person, because it can feel like giving up on them. People also stretch it, with a sigh or a joke, to someone who will not listen and will not change. It does not mean the person knows little; that is uneducated. It means teaching does not seem to work.