This is the 10158th most frequent Polish word.
boleśnie
"Painfully."
Here, 'boleśnie' describes the manner in which the action (hitting) was experienced, emphasizing the resultant pain.
Chłopiec boleśnie uderzył się o stół.
The boy painfully hit himself on the table.
In this sentence, 'boleśnie' conveys an emotional intensity related to the feeling of loss.
Boleśnie odczuliśmy stratę ukochanego psa.
We painfully felt the loss of our beloved dog.
Here, 'boleśnie' is used metaphorically to describe the significant difficulty endured during the process.