This is the 11807th most frequent Polish word.
kostiumach
"Kostiumach" is the locative plural form of "kostium," meaning "costumes" in English.
Here, 'kostiumach' is in the locative case to indicate the location or circumstance of wearing the costumes.
Aktorki występowały w różnokolorowych kostiumach.
The actresses performed in multicolored costumes.
In this sentence, 'kostiumach' is in the locative case indicating the state or condition of being in costumes.
Postacie w tych filmach zawsze są w dawnych kostiumach.
The characters in these films are always in old-fashioned costumes.
Here, 'kostiumach' once again uses the locative case to describe the situation regarding the costumes seen.