noun
eldest son's descendants; lineal descendants through the eldest son
Formal term used in legal, historical, or family-register contexts referring to the direct line of descent from the eldest son. Not an everyday word.
旧民法では、嫡孫が家督を継ぐことが定められていた。
Under the old Civil Code, it was stipulated that the lineal descendants of the eldest son would succeed to the family headship.
Compound of 嫡 (ちゃく, 'legitimate heir') and 孫 (そん, 'grandchild/descendant'). The exact historical derivation is uncertain, but the term has been used in Japanese legal and family contexts to denote the line of descent from the eldest son.