This is the 2805th most frequent Polish word.
jakąś
The Polish word "jakąś" means "some" or "a certain" (feminine singular accusative form).
In this sentence, 'jakąś' refers to an indeterminate book, meaning it doesn't specify which book but rather any book the person might have.
Czy masz jakąś książkę do pożyczenia?
Do you have a book to lend me?
Here, 'jakąś' describes 'kobietą' (woman) and indicates that this particular woman is not known or specified.
Spotkałem się z jakąś kobietą w parku.
I met with some woman in the park.
In this instance, 'jakąś' relates to 'sensowną godzinę' (reasonable hour), suggesting an unspecified but reasonable time for the action.