This is the 4462nd most frequent Polish word.
kieszeni
"Kieszeni" means "pocket" in the genitive or locative case in Polish.
In this sentence, 'kieszeni' is used in the locative case to indicate the location where the money is.
Mam pieniądze w kieszeni.
I have money in the pocket.
Here, 'kieszeni' is used in the genitive case to indicate possession or relation.
Pieniądze wypadały z jego kieszeni.
The money was falling out from his pocket.
In this context, 'kieszeni' is used in the genitive case to describe a characteristic or attribute of the pocket.