This is the 707th most frequent Finnish word.
uuden
"Uuden" means "of the new" in English.
In this sentence, 'uuden' is the genitive form of 'uusi', modifying 'auton' to mean 'new car'.
Ostin uuden auton.
I bought a new car.
The word 'uuden' is the accusative case of 'uusi' (new), modifying the object 'auton' (car) and indicating that the car being referred to is new.
Ostin uuden auton.
I bought a new car.
Here, 'uuden' describes 'vuoden' (year) in the genitive case, indicating possession and that the year referred to is new.