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妹
imōto
younger sister
私の妹は学生です。
My younger sister is a student.
neutral
A female sibling younger than oneself.
妹が一人います。
I have one younger sister.
妹と一緒に買い物に行きました。
I went shopping with my younger sister.
Used regardless of age difference if the speaker is older. For siblings of unknown age, use '姉妹' (sisters).
Pro Tip
Age hierarchy in Japanese family terms
Always use '妹' if you are older. If you are younger, use '姉' for your older sister. For siblings of unknown age, '姉妹' (sisters) is neutral.
Word Origin
From Old Japanese *imo₂to₂ (younger sister), compound of *imo (young, beloved) + *to (person).
Usage Notes
Avoid using '妹' to refer to someone else's younger sister unless close; use '妹さん' (polite) or 'お姉さんの妹さん' (your younger sister). In formal contexts, '末の妹' (my youngest sister) may be used.
Word Breakdown
妹
younger sister
root和英辞典