isinpäätteen

Isinpäätteen is a Finnish term that translates to "father's suffix" or "paternal suffix." It refers to a specific type of patronymic naming convention historically used in Finland. In this system, a child's surname was derived from their father's given name. The father's name was typically followed by a suffix, most commonly "npoika" (son of) or "ntytär" (daughter of). For example, if a father's name was Jussi, his son might be named Matti Jussinpoika and his daughter Liisa Jussintytär.

This practice was prevalent until the late 19th and early 20th centuries when a unified surname law was introduced in Finland. This law encouraged or mandated the adoption of fixed, inherited surnames, moving away from the traditional patronymic system. While the isinpäätteen system is no longer in common use for official surnames, remnants of it can still be found in historical records and sometimes in cultural contexts. It provides valuable insight into Finnish social history and naming traditions. The transition to fixed surnames aimed to standardize identification and facilitate administrative processes.