The ordinary meaning of is younger sister, but in ancient time, it meand beloved girl, thus meant a couple in love and then wife and husband. Nowadays this.
弟, おとうと, otouto, Younger Brother. 16. 妹, いもうと, imouto, Younger Sister. 17. 夫婦, ふうふ, fuufu, Married Couple / Husband and Wife. 18. 主人, しゅじん.
Words for family members and other relatives in Japanese. husband, 夫 (otto) - inf 主人 (shujin) 亭主 (teishu) wife, 妻 (tsuma) - inf older sister, 姉 (ane) - inf
One's brother-in-law or sister-in-law's sister; that is, one's sibling's spouse's sister (one's sister's husband's sister or one's brother's wife's sister). (in the plural).