This is the 11500th most frequent Polish word.
jesienna
"Jesienna" means "autumnal" or "related to autumn."
Here, 'jesienna' is an adjective describing 'pogoda' (weather), expressing its relation to the fall season.
Jesienna pogoda jest piękna, pełna kolorowych liści.
The autumn weather is beautiful, full of colorful leaves.
In this context, 'jesienne' modifies 'zachody słońca' (sunsets), identifying the type of sunsets typical for autumn.
Spędzamy wieczór oglądając jesienne zachody słońca.
We spend the evening watching autumn sunsets.
'Jesienne' here is used to describe 'spacery' (walks), emphasizing that they occur during the autumn season.