This is the 11977th most frequent Polish word.
kąpielowych
"Of bathing" or "bath" (adjective, genitive plural form).
In this sentence, 'kąpielowe' serves as an adjective associated with 'spodenki' (shorts), indicating shorts intended for bathing purposes.
Kupiłem nowe spodenki kąpielowe na wakacje.
I bought new bathing shorts for the holiday.
Here, 'kąpielowych' describes 'kostiumów' (costumes), specifying that these are costumes used for swimming or bathing.
W sklepie widziałem różne modele kostiumów kąpielowych.
I saw various models of swimwear in the store.
In this instance, 'kąpielowe' modifies 'ręczniki' (towels), describing them as towels used for bathing or similar activities.