This is the 936th most frequent Finnish word.
uusien
"Uusien" is the genitive plural form of "uusi," meaning "of new" or "of the new ones."
In this sentence, 'uusien' is the genitive plural form of 'uusi', used to describe possession or characteristics related to new things, specifically books.
Ostin kirpputorilta paljon uusien kirjojen kaltaisia esineitä.
I bought many items similar to new books from the flea market.
Here, 'uusien' is used to modify 'ystäviemme' (our friends), indicating that the friends are new. It's again in the genitive plural form.
Juhlimme uuden vuoden aattoa uusien ystäviemme kanssa.
We celebrated New Year's Eve with our new friends.
In this example, 'uusien' modifies 'teosten' (works), showing that the works are new. The word follows the genitive case linking it to artists' works.