This is the 1527th most frequent Polish word.
amunicji
"Ammo" or "ammunition."
In this sentence, 'amunicji' is the genitive form used after 'zapas' to denote possession or relation.
Żołnierze przygotowywali zapas amunicji przed bitwą.
The soldiers prepared a supply of ammunition before the battle.
Here, 'amunicji' is the genitive form used to denote the quantity of an uncountable noun with 'ilości'.
Nie mamy wystarczającej ilości amunicji do kontynuowania walki.
We don't have enough ammunition to continue the fight.
In this context, 'amunicji' is used in its genitive form following 'pełną' to indicate its content.