ancestor XIII. Early forms are of three types: (i) auncetre, surviving XVII in latinized sp. auncitor; (ii) ancestre, antecedent of the present form through ancestour, by assim. to -tour, -TOR; (iii) ancessour (rare). — OF. ancestre (mod. ancêtre) orig. nom. :- L. antecēssor, and OF. ances(s)our acc. :- L. antecēssōrem predecessor, f. antecēdere precede, f. ante before + cēdere go (cf. CEDE).
So ancestry XIV. Modification, after ancestre, of OF. ancesserie, f. ancessour.

an·ces·tor / ˈanˌsestər/ • n. a person, typically one more remote than a grandparent, from whom one is descended. ∎  an early type of animal or plant from which others have evolved. ∎  an early version of a machine, artifact, system, etc., that later became more developed.

ancestor of a node in a tree. Any node on the unique path from the root of the tree to the node in question. A proper ancestor of a node, A, is a node, B, such that B is an ancestor of A and A ≠ B. See also parent.