firstborn       
adjective, noun [ C usually singular ]  literary or humorous uk/ˈfɜːst.bɔːn/ us/ˈfɝːst.bɔːrn/
 头胎;长子;长女
used to refer to the first child of a set of parents
  In the Hebrew Bible, the firstborn son is the one who inherits his father's position as head of the family. 根据《希伯来圣经》,长子是继承父亲家庭首领位置的人。 
 Olaf is my firstborn. 奥拉夫是我的第一个孩子。 
 Synonym: eldest