This is the 7206th most frequent Polish word.
jasińskiego
"Jasińskiego" is the genitive or accusative singular form of the Polish surname "Jasiński," typically meaning "of Jasiński" or "Jasiński's."
The word 'Jasińskiego' here is a possessive genitive form, indicating ownership by someone named Jasiński.
Wczoraj odwiedziliśmy mieszkanie Jasińskiego.
Yesterday we visited Jasiński's apartment.
In this context, 'Jasińskiego' is the genitive form used after 'Pani,' which is often done in Polish to show respect when referring to a person's last name.
Pani Jasińskiego uczyła mnie matematyki w szkole.
Mrs. Jasiński taught me mathematics at school.
Here, 'Jasińskiego' is the genitive case form after the preposition 'od,' indicating the origin of the letter as being from Mr. Jasiński.