This is the 7343rd most frequent Polish word.
kasią
"Kasią" is not a standalone Polish word but may be a form of the name "Kasia," which is a diminutive of Katarzyna (Catherine).
In this sentence, 'Kasią' is used in the instrumental case form of the proper noun 'Kasia', a female name, indicating accompaniment.
Spotkałem się wczoraj z Kasią w parku.
I met with Kasia yesterday in the park.
Here, 'Kasią' again appears in the instrumental case, used when implying communication or interaction with another person.
Rozmawiam przez telefon z Kasią.
I am talking on the phone with Kasia.
In this context, 'Kasią' is utilized in the instrumental case to denote the person accompanying the speaker during the activity.