Source : Webster's Revised Unabridged Dictionary (1913)

Ancestor \An"ces*tor\, n. [OE. ancestre, auncestre, also
   ancessour; the first forms fr. OF. ancestre, F. anc[^e]tre,
   fr. the L. nom. antessor one who goes before; the last form
   fr. OF. ancessor, fr. L. acc. antecessorem, fr. antecedere to
   go before; ante before + cedere to go. See {Cede}, and cf.
   {Antecessor}.]
   1. One from whom a person is descended, whether on the
      father's or mother's side, at any distance of time; a
      progenitor; a fore father.

   2. (Biol.) An earlier type; a progenitor; as, this fossil
      animal is regarded as the ancestor of the horse.

   3. (Law) One from whom an estate has descended; -- the
      correlative of heir.

Source : WordNet®

ancestor
     n : someone from whom you are descended (but usually more remote
         than a grandparent) [syn: {ascendant}, {ascendent}, {antecedent},
          {root}] [ant: {descendant}]