This is the 608th most frequent Finnish word.
syksyn
"Syksyn" means "of autumn" or "of fall" in English.
In this sentence, 'syksyn' is a possessive form used to indicate that the leaves belong to or are associated with autumn.
Syksyn lehdet ovat kauniin värisiä.
The autumn leaves are beautifully colored.
In this context, 'syksyn' functions as a temporal expression, indicating the time period during which the action takes place, as an equivalent to 'during autumn'.
Syksyn aikana päivät lyhenevät.
During autumn, the days get shorter.
The word 'syksyn' in this sentence is used as a possessive adjective modifying 'lehden', indicating that the leaf belongs to or is characteristic of the autumn.