real surname; original family name
Refers to one's true or original family name, as opposed to an alias, pen name, or married name. Often used in historical or formal contexts.
He uses a pen name, but his real surname is Tanaka.
My surname changed when I got married, but my original family name is Yamada.
Compound of 本 (ほん, 'true, real, original') and 姓 (せい, 'surname, family name').