妹|いもうとimouto[4]odaka (tail-high)

1. nounyounger sister
   あのかわいい少女しょうじょは私の妹いもうとです。↗

   That pretty girl is my sister.

• Related妹君いもうとぎみFormalA formal, old-fashioned honorific for another person's younger sister; rarely heard today — say 「妹さん」 in everyday speech.
• Related妹さんいもうとさんNeutralA polite, common way to refer to someone else's younger sister; for your own sister, use 「妹」.
• Antonym姉あねNeutralThe opposite of 「妹」: an older sister. To refer to someone else's older sister, use 「お姉さん」.

Use 「妹」 for your own younger sister and 「妹さん」 for someone else's; 「妹君」 is an old-fashioned formal alternative. 「姉」 is the opposite, meaning older sister.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. （いもうと）同おなじ親おやから産うまれた年下とししたの女性じょせい。または、配偶者はいぐうしゃにとっての妹いもうと。年上としうえは姉あねという。