This is the 9455th most frequent Polish word.
wasielewski
"Wasielewski" is a Polish surname; it does not have a specific standalone definition in English.
Here, 'Wasielewski' is used as a surname to refer to an individual.
Wasielewski mieszka w Warszawie.
Wasielewski lives in Warsaw.
In this sentence, 'Wasielewskich' refers to the plural genitive case of the surname Wasielewski, indicating the family.
Rodzina Wasielewskich przyjechała do miasta.
The Wasielewski family arrived in the city.
Here, 'Wasielewskiego' is the singular accusative form of the surname Wasielewski used to denote the direct object.