This is the 2315th most frequent Polish word.
warmińsko
"Warmińsko" refers to something related to the region of Warmia in Poland.
The word 'warmińsko' is used as part of the compound adjective 'warmińsko-mazurskie', describing something related to the regions of Warmia and Mazury.
Odwiedziłem warmińsko-mazurskie jeziora.
I visited the Warmian-Masurian lakes.
Here, 'warmińsko' functions adverbially, modifying 'urządzonej' to describe the style of decor as being typical of Warmia.
Spotkaliśmy się na warmińsko urządzonej działce.
We met on a plot decorated in a Warmian style.
In this sentence, the term 'warmińsko' is treated as a noun-like term signifying the Warmia region.