Refers specifically to an older sister-in-law: either the speaker's spouse's older sister, or the wife of the speaker's older brother. The reading is ぎし; the gikun reading あね is rare and archaic.
義姉は来月、結婚するそうです。
I hear my sister-in-law is getting married next month.
She is my older sister-in-law.
兄の妻、つまり義姉が料理を教えてくれた。
My older brother's wife, that is, my sister-in-law, taught me how to cook.
older stepsister; older adopted sister; non-blood-related older sister
Used for an older female sibling who is not related by blood, such as a stepsister, adopted sister, or a close non-blood-related older sister figure. Less common than the sister-in-law sense.
彼女は私の義姉で、父の再婚相手の連れ子です。
She is my older stepsister, the child of my father's new spouse.
義姉として育った彼女は、実の姉のように感じる。
Having grown up as my non-blood-related older sister, she feels like a real older sister to me.
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.
義姉 is the female term for an older sister-in-law, whereas 義兄 is the male counterpart meaning an older brother-in-law; the shared 義-prefix makes them easy to confuse.
Used to politely count people, such as one's older sister-in-law (義姉).
Standard kanji spelling for the reading ぎし.
A Sino-Japanese compound of 義, marking a relationship established by marriage or adoption, and 姉 “elder sister.”