This is the 4082nd most frequent Polish word.
archiwów
"Archiwów" means "archives" (genitive plural form).
Here, 'archiwów' is the genitive plural form of 'archiwum', referring to the archives being searched through.
Przeglądaliśmy katalog archiwów w poszukiwaniu starych dokumentów.
We were browsing the archive catalog in search of old documents.
In this context, 'archiwów' is again the genitive plural form, used to denote the collections being amassed by the library.
Biblioteka gromadzi wiele archiwów z różnych epok.
The library collects many archives from different eras.
Here, 'archiwów' is used to indicate the source or location (archives) where information is being sought.