This is the 1885th most frequent Polish word.
opolskiego
"Opolskiego" means "of Opole" or "relating to Opole," referring to the Opole region in Poland.
In this sentence, "opolskim" refers to the adjectival form of "Opole," describing the voivodeship.
Mieszkałem przez kilka lat w województwie opolskim.
I lived for several years in the Opole voivodeship.
Here, "opolskiego" modifies "regionu," indicating possession or association with Opole.
Tradycje kulinarne opolskiego regionu są bardzo bogate.
The culinary traditions of the Opole region are very rich.
In this case, "opolskiego" describes the duke as being from or associated with Opole.