長女
ちょうじょ · choujo · JLPT N2 · noun
daughter
👧 長 = eldest or chief, 女 = daughter: 長女 = eldest + daughter
長 also means long or leader, so the first-born daughter leads the sibling line. 女 is the woman radical, which appears in many family terms like 母 and 姉.
女 — pictograph of a kneeling woman
女 is a pictograph originating in oracle bone script, depicting a person kneeling with arms crossed in front, a posture associated with women in ancient China. Over time the form was simplified and squared off into the modern character. Its core meaning of 'woman' or 'female' has remained stable for over three thousand years.