This is the 685th most frequent Polish word.
broń
Weapon.
'Broń' is used here as a noun meaning 'weapon'.
Broń jest używana do ochrony.
A weapon is used for protection.
'Broń' here is a verb, a form of 'bronić', which means 'to defend'.
Nie broń go, jeśli wiesz, że się myli.
Do not defend him if you know he is wrong.
'Broni' is a noun in the genitive singular form of 'broń' used to indicate possession or association.