lineal       
adjective  formal uk/ˈlɪn.i.əl/ us/ˈlɪn.i.əl/
 直系的
relating to a person's lineage (= the members of a person's family who are directly related to that person and who lived a long time before him or her)
  She claims lineal descent from Henry VIII. 她自称是亨利八世的直系后人。 
 A "relative" is the spouse, parent, brother or sister, or remoter lineal ancestor of the person. “亲属”是指当事人的配偶、父母、兄弟姐妹或更远的直系祖辈。 
 See: lineage
 - More examples
 - King Carlos II died without a lineal heir.
 - Native Hawaiians are defined as direct lineal descendants of indigenous peoples who lived on the islands before 1893.
 - The lineal descendants of Hamilton and Burr plan to gather on the waterfront and reenact this most famous of American duels.