If someone is astute, they understand a situation or someone’s behaviour very well and very quickly — especially in a way that helps them get an advantage. It is more than “clever.” A clever student knows the answer; an astute one also sees what the teacher is really asking, or which choice will help later. The word often carries a slight edge: sharp, a bit worldly, not naive. You can praise a business person or a politician as astute without calling them kind. It is a grown-up, slightly formal adjective; children rarely need it. Though actually, in kind praise it can just mean “you read the room well,” with less of the “for your own gain” flavour — tone decides.