ちょうなん長男chounan
1.
The male child who is born first in a family, often carrying specific responsibilities or expectations within traditional family structures.
2.
The oldest male sibling among brothers, distinguished from younger brothers within the same family.
3.
The first son in a family, who may hold a significant role in family lineage or inheritance matters.
Example:
彼は私の長男の名付け親であった。