Learn Finnish: Se oli nälkävuosi, jolloin isoisästä tuli siirtolainen. - It was a year of famine when grandfather became an immigrant.

Kun is a conjunction used to link two events happening at the same time. Jolloin, however, is a relative adverb that must refer back to a specific time-related noun in the previous clause. Here, it points directly back to nälkävuosi (year of famine), acting like "during which".

Why is "grandfather" written as isoisästä with the -stä ending?

When expressing that someone or something becomes something, Finnish uses the verb tulla and puts the starting subject in the elative case (-sta or -stä, normally meaning "out of"). So, isoisästä tuli siirtolainen literally translates to "out of grandfather came an immigrant."

How does the word nälkävuosi break down?

It is a compound word made of nälkä (hunger) and vuosi (year). In Finnish, a "hunger year" is the standard historical term used to describe a year of famine.

Does siirtolainen mean immigrant or emigrant?

It broadly covers both! A siirtolainen is a migrant who moves to another country for permanent settlement. If you need to be highly specific, an immigrant is a maahanmuuttaja (mover into the country) and an emigrant is a maastamuuttaja (mover out of the country).