also: ほんぷく
noun
legitimate child; child born in wedlock
Refers to a child born to a legal wife, as opposed to a child born to a concubine or out of wedlock. This term is historical and rarely used in modern Japanese outside of historical or literary contexts.
江戸時代、本腹の子だけが家督を継げた。
In the Edo period, only legitimate children could inherit the family headship.
彼は本腹の子として育てられたが、実は側室の子
He was raised as a legitimate child, but in fact he was the child of a concubine.
Compound of 本 (hon, 'main' or 'real') and 腹 (hara, 'belly' or 'womb'), literally meaning 'true womb', referring to birth from the legal wife.