lineal

This term carries a heavy legal and genealogical weight, specifically referring to a straight line of descent from parent to child. It is strictly used to describe the biological or legal vertical path of a family tree, avoiding any side branches like cousins or aunts. In contrast to linear, which describes a physical line or a sequence of events, lineal is almost exclusively reserved for ancestry and hereditary rights. It evokes an image of a singular, unbroken chain of bloodline and legitimacy.