Translation guide
In Japanese, how you refer to your younger sister depends on the social context—whether you're talking about her to others, addressing her directly, or referring to someone else's younger sister. The most common word is 妹 (いもうと), but in direct address, older siblings usually call younger sisters by their given name or a nickname.
You want to mention your younger sister in a conversation with someone outside your family.
The standard, neutral word for 'younger sister' when referring to your own. Use this when talking about her to people outside your family.
You want to call your younger sister to get her attention or talk to her.
In Japanese families, older siblings typically address younger siblings by their given name (often with -ちゃん for girls) or a family nickname. Using 妹 (いもうと) to address her directly would sound unnatural.
花子、ちょっと来て。
Hanako, come here a sec.
花ちゃん、宿題やった？
Hana-chan, did you do your homework?
You want to talk about a friend's or acquaintance's younger sister.
Add さん to 妹 to show respect when referring to someone else's younger sister. This is polite and standard.
田中さんの妹さんは医者だそうですね。
I hear that Mr. Tanaka's younger sister is a doctor.
In casual conversation among close friends, you can drop さん, but it's safer to use 妹さん.
You want to refer to younger sisters as a category, or to multiple younger sisters.
The word 妹 can be used generically. For plural, Japanese often doesn't mark plural explicitly, but you can use 妹たち (いもうとたち) or 姉妹 (しまい) for 'sisters'.
妹はたいてい姉より背が高い。
Younger sisters are usually taller than older sisters.
彼は妹たちにプレゼントを買った。
He bought presents for his younger sisters.
You need to refer to a younger sister in a formal document, speech, or literary work.
Even in formal contexts, 妹 is appropriate. There is no special honorific form for one's own younger sister when speaking formally about her.
私の妹は現在海外に留学しております。
My younger sister is currently studying abroad.
Calling your younger sister 妹 (いもうと) to her face is unnatural. Use her name or a nickname instead.
Adding ちゃん to a younger sister's name (e.g., 花ちゃん) is common and affectionate, especially for young girls. For teenagers or adults, you might just use the name without an honorific.
Kenta's younger sister is cute, isn't she.