This is the 14245th most frequent Polish word.
prokuratorem
"Prokuratorem" means "prosecutor" in English.
The word 'prokuratorem' is the instrumental case of the noun 'prokurator' (prosecutor), used here to denote the role or profession acquired by the subject.
On został prokuratorem w sądzie.
He became a prosecutor in the court.
Here, 'prokuratorem' is used to indicate the person with whom the conversation occurs, in the instrumental case showing the entity involved.
Rozmawiałem z prokuratorem o sprawie.
I spoke with the prosecutor about the case.
In this sentence, 'prokuratorem' is instrumental case indicating the title awarded to Jan Kowalski.