noun
sisters of the same mother; uterine sisters
Refers to sisters who share the same mother, often used in contexts distinguishing full siblings from half-siblings.
彼女たちは同母姉で、とても仲が良い。
They are sisters of the same mother and get along very well.
姉妹 is the general term for sisters, without specifying maternal relationship.
Compound of 同母 (same mother) and 姉 (older sister). The exact historical derivation is uncertain, but the term is formed from standard Sino-Japanese elements.