This is the 9513th most frequent Polish word.
wilków
"Wilków" means "of wolves" or refers to a place name in Poland.
In this sentence, 'wilków' is the genitive plural form of 'wilk,' used to indicate the object of fear, following the verb 'obawiam się' which requires the genitive case.
Obawiam się wilków, które zamieszkują ten las.
I am afraid of wolves that inhabit this forest.
Here 'wilków' is in the genitive plural case, showing possession or relation to the activity 'wycia' (howling).
Słuchaliśmy wycia wilków w środku nocy.
We listened to the wolves' howling in the middle of the night.
This sentence uses 'wilków' in the genitive plural form, after the verb 'nie widziałem,' which requires the genitive case in negative expressions.