妹；妹子；娣；女弟;
例句
1.My younger sister is too young to dress herself.
我妹妹太小了，還不會自己穿衣服。
2.My younger sister's teachers just took phones away.
現在我妹妹的老師會直接把手機沒收。
3.Robert's taken a fancy to your younger sister.
羅伯特開始對妳的小妹妹著迷了。