noun, noun which may take the genitive case particle 'no'
born of the same mother; same mother
Used to describe siblings who share the same mother, often in contrast to half-siblings or step-siblings. Somewhat formal or literary.
彼らは一腹の兄弟だ。
They are brothers born of the same mother.
一腹の姉妹として育った。
They grew up as sisters from the same mother.