Denshi Jisho — Online Japanese dictionary

妹 いもうと younger sister
Common word, Noun, Humble (kenjougo) language 
義妹 いもうと sister-in-law (younger); stepsister
Irregular kana usage, Noun 
妹背鳥 いもせどり 1: (Obscure term) any bird of family Motacillidae (excluding the pipits);
2: lesser cuckoo (Cuculus poliocephalus)
Noun 
妹分 いもうとぶん protegee; someone who one considers as a younger sister
Noun 
妹婿 いもうとむこ the husband of one's younger sister
Noun 
妹さん いもうとさん younger sister
Noun, Honorific or respectful language 
妹の命 いものみこと young lady
Noun, Archaism, Obscure term, Honorific or respectful language 
妹娘 いもうとむすめ younger daughter
Noun 

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