sister-in-law (spouse's younger sister or younger brother's wife)
Refers specifically to a younger sister-in-law by marriage. For an older sister-in-law, 義姉 (ぎし) is used.
My sister-in-law is still a university student.
My younger brother's wife, that is, my sister-in-law, helped with the cooking.
younger stepsister; younger adopted sister; non-blood-related younger sister
Used for a younger sister who is not related by blood, such as through remarriage or adoption. The reading いもうと is a gikun reading sometimes used for this sense, but ぎまい is standard.
I got a younger stepsister through my father's remarriage.
My adopted younger sister and I aren't related by blood, but I think of her as a real sister.
My older brother got married, and now I have a sister-in-law.
I get along well with my sister-in-law, so we often go out together.
妹 is a biological younger sister, whereas 義妹 is a younger sister by marriage or remarriage/adoption, not by blood.
義姉 means an older sister-in-law (or older non-blood sister), while 義妹 means a younger sister-in-law (or younger non-blood sister); the kanji look almost identical, so learners often swap them.
義弟 refers to a younger brother-in-law, while 義妹 is the corresponding term for a younger sister-in-law; the two are easy to mix up in writing.
Standard kanji spelling for both senses.
Compound of 義 (ぎ, 'non-blood, in-law') and 妹 (まい, 'younger sister'). The reading いもうと for 義妹 is a gikun (meaning-based reading) applied to the kanji compound.