This is the 13258th most frequent Polish word.
opolskich
"Opolskich" refers to "of Opole" or "related to Opole," a region or city in Poland.
The word 'opolskich' here relates to customs or traditions originating from the Opole region, functioning as an adjective in the sentence.
Spotkałem się z opolskimi zwyczajami podczas mojej podróży na południe Polski.
I encountered Opole traditions during my trip to the south of Poland.
In this sentence, 'opolskich' modifies 'villages', indicating their geographical association with the Opole area.
Wszyscy mieszkańcy opolskich wsi świętowali doroczne festyny.
All residents of the Opole villages celebrated the annual festivals.
Here, 'opolskich' describes 'books', denoting their thematic or regional affiliation with Opole.