This is the 462nd most frequent Finnish word.
kehityksen
"Of development" or "of progress."
In this sentence, 'kehityksen' is in the genitive case of 'kehitys', meaning 'development'. It is used to form a possessive structure together with 'kestävä' ('sustainable'), referring to a particular kind of development.
Kestävän kehityksen tavoitteet ovat tärkeitä.
The goals of sustainable development are important.
Here, 'kehityksen' is also in the genitive case, serving to describe for whose or what benefit ('hyväksi' translates to 'for the good') the actions are being performed.
Hän tekee kaiken kehityksen hyväksi.
He does everything for the sake of development.
In this sentence, 'kehityksen' modifies 'suunnitelma' ('plan'), linking 'development' to the city, indicating it refers to a specific development related to the city.