This is the 4431st most frequent Polish word.
jesienne
"Jesienne" means "autumnal" or "related to autumn."
The word 'jesienne' here is used as an adjective to describe 'liście' (leaves), indicating that they pertain to the autumn season.
Jesienne liście spadają z drzew.
Autumn leaves are falling from the trees.
In this sentence, 'jesienne' describes 'wieczory' (evenings), again highlighting their characteristic nature related to the season of autumn.
Jesienne wieczory są chłodne i nostalgiczne.
Autumn evenings are cool and nostalgic.
Here, 'jesienne' modifies 'kolory' (colors), specifying the particular hues and tones typical of autumn.