eldest
/ˈeldɪst; `ɛldɪst/ adj[attrib 作定语], n (of people,esp of three or more closely related members of a family) first-born; oldest （指人, 尤指家中同辈的至少三个成员中的）第一个出生的, 年长的
Jill is my eldest daughter. 吉尔是我的长女.
Jill is the eldest of my three children. 吉尔是我三个孩子中年龄最大的.
Jill is the eldest of three, ie the oldest child in a family with three children. 吉尔是一家三个孩子中最大的.
Jill is my eldest. 吉尔是我的大孩子. =>Usage at elder1 用法见elder1.