This is the 16628th most frequent Polish word.
wrześniowe
"Wrześniowe" means "September-related" or "of September."
The term 'wrześniowe' is used as an adjective to describe the evenings occurring in September.
Wrześniowe wieczory są chłodne i pełne nostalgii.
September evenings are cool and full of nostalgia.
Here, 'wrześniowe' modifies 'spacery' (walks), indicating that the walks take place or are characteristic of the month of September.
Uważam, że wrześniowe spacery po parku mają w sobie coś magicznego.
I think September walks in the park have something magical about them.
In this sentence, 'wrześniowe' is used to characterize 'liście' (leaves) as being associated with the month of September.