This is the 4563rd most frequent Polish word.
listem
"Listem" means "a letter" (as in written correspondence) in Polish, in the instrumental case.
In this sentence, 'listem' is used to refer to the instrument or means (a letter) utilized to fulfill an action.
Odpowiem na Twoje pytanie listem.
I will respond to your question with a letter.
Here, 'listem' indicates the medium (a letter) through which information is conveyed.
Posłaniec przekazał wiadomość listem.
The messenger delivered the message with a letter.
This usage of 'listem' refers to a specific letter as an entity within the context of interaction or handling.