Your stepsister is a girl or woman who became your sister because a parent of yours married a parent of hers. You two share no blood at all — her mother married your father, or her father married your mother, and now you live in one family.

Your stepsister你的stepsister is a girl or woman是一個女生或女人 who became your sister因為...而變成你的姊妹 because a parent of yours married a parent of hers你的一位家長娶了／嫁了她的一位家長。You two share no blood at all你們兩個完全沒有血緣關係 — her mother married your father她媽媽嫁給你爸爸, or her father married your mother或她爸爸娶了你媽媽, and now you live in one family現在你們住在同一個家庭裡。

This is the key thing: a stepsister and you have no parent in common. That is what separates her from a half-sister, who shares one real parent with you (the same mother, or the same father). English keeps those two words apart carefully, and it matters to people who have them.

This is the key thing重點就在這裡: a stepsister and you have no parent in common stepsister跟你沒有共同的親生家長。That is what separates her from a half-sister這就是她跟half-sister的差別, who shares one real parent with you half-sister跟你有一位共同的親生家長 (the same mother, or the same father同一個媽媽，或同一個爸爸)。English英文 keeps those two words apart carefully很小心地把這兩個字分開, and it matters to people who have them對真正有這種關係的人來說，這件事很重要。

Most English speakers know the word first from Cinderella, where the stepsisters are cruel — so the word carries a faint bad smell in stories that it does not deserve in real life.

Most English speakers know the word first from Cinderella大部分英語使用者第一次認識這個字是從《灰姑娘》來的, where the stepsisters are cruel故事裡的stepsisters很殘忍 — so the word carries a faint bad smell in stories所以這個字在故事裡帶著一點負面味道 that it does not deserve in real life但這在現實生活裡是不應該的。

Real stepsisters are often close, and many people simply say 'my sister' and skip the step- entirely once the family has settled. You would use the full word 'stepsister' mainly when you need to explain the family clearly to someone outside it.

Real stepsisters現實中的stepsisters are often close常常感情很好, and many people simply say 'my sister'很多人乾脆直接說「my sister」 and skip the step- entirely完全省略step-這個字首 once the family has settled等家庭穩定下來以後。You would use the full word 'stepsister'你會用完整的「stepsister」這個字 mainly when you need to explain the family clearly to someone outside it主要是在需要向家庭以外的人講清楚關係的時候。

It is written as one word nowadays; 'step-sister' with a hyphen turns up in older books and is not wrong, just old-fashioned.

It它 is written as one word nowadays現在通常寫成一個字; 'step-sister' with a hyphen有連字號的「step-sister」 turns up in older books會出現在比較舊的書裡 and is not wrong, just old-fashioned這樣寫並沒有錯，只是比較舊式。