Learn Finnish: Hallitus tekee tärkeän päätöksen. - The government makes an important decision.

Päätös comes from the verb päättää (to decide). By taking the verb stem and adding the result suffix -ös, the action of deciding becomes a noun: a decision. Vowel harmony dictates the use of -ös instead of -os because the verb stem has front vowels (ä).

Is hallitus (government) also a derived noun?

Yes! It comes from the verb hallita (to rule or govern). The suffix -us is added to the verb stem to create a noun representing the entity doing the action or the result of the action, which gives us hallitus (the government).

Why do both tärkeä and päätös end in -n here?

They form the direct object of the sentence. Because making a decision is a completed action that produces a whole, single result, the object takes the accusative case, which looks exactly like the genitive ending -n. The adjective tärkeä must match the case of the noun it describes.

What happens to the stem of päätös when we add the -n ending to make päätöksen?

Nouns ending in -os or -ös undergo a stem change where the final -s becomes -kse- before an ending is attached. So the base form päätös becomes the stem päätökse-, and adding the object marker -n gives us päätöksen.