This is the 852nd most frequent Finnish word.
kauan
"Long" or "for a long time."
Here, 'kauan' is used to ask about the duration of time for an action.
Kuinka kauan sinä odotit?
How long did you wait?
In this sentence, 'kauan' is used to refer to the duration of the journey in question.
Hän ei tiedä, kuinka kauan matka kestää.
They don't know how long the journey will take.
Here, 'kauan' indicates the expected short duration of an event.