also: きょうだい
older sister and younger brother
Refers specifically to a sibling pair consisting of an older sister and a younger brother. Not used for other sibling combinations.
They are an older sister and younger brother; the sister is a university student and the brother is a high school student.
The older sister and younger brother went shopping together.
姉弟 refers to an older sister and younger brother, whereas 弟妹 refers to a younger brother and younger sister, making the two easy to confuse due to their similar kanji patterns.
Standard kanji spelling for the reading してい, specifically meaning an older sister and younger brother pair.
Gikun reading; the kanji 姉弟 is normally read してい. Reading it as きょうだい is a special, non-standard reading used in some contexts to emphasize the sibling relationship, but it is uncommon.
Compound of 姉 (older sister) and 弟 (younger brother). The reading してい is the standard on'yomi combination. The gikun reading きょうだい is a special reading applied to this kanji compound to convey the meaning of siblings, but it is not the standard reading.