Kind-hearted describes a person whose first move is to be warm and generous — they notice when you are struggling and they want to help. It is about the feeling in them, not only polite manners. A kind-hearted person may not be rich; they share time, a seat, a kind word. Though actually, English has many -hearted words (cold-hearted, hard-hearted, warm-hearted), and kind-hearted sits on the soft, approving side. It is friendly, a little warm and old-fashioned, fine in speech and in writing. You can also write kindhearted as one word; the little line in the middle is common and clear. Kindly is close, but it can just mean polite, or even 'please, would you…'; kind-hearted always points to a generous nature.