Rightful means this is who or what should have it, by law or by what is fair. We say the rightful owner of a bag, the rightful heir to a title or a house, a singer's rightful place on the stage. The feeling is this belongs here; the claim ought to be honoured. It is a little formal. In daily talk people often say the real owner or who it belongs to. Though actually, speakers also use it with a sigh of relief, as if the world has been set straight: back in its rightful place. It does not mean factually correct — a maths answer is right, not rightful.

應有的；正當的（rightful owner＝東西本來該屬於的那個人）