noun
younger half-sister (different mother)
Refers specifically to a younger sister who shares the same father but has a different mother. Used in family registers and formal contexts.
彼女は私の異母妹です。
She is my younger half-sister from a different mother.
戸籍上は異母妹にあたる。
She is legally my younger half-sister (different mother).
Refers to a younger half-sister with a different father, whereas 異母妹 shares the same father but a different mother.
Compound of 異母 (different mother) and 妹 (younger sister).