This is the 12497th most frequent Russian word.
книжный
Relating to books.
The word 'книжный' is used as an adjective describing 'шкаф', indicating that the cabinet is designated for holding books.
Я купил книжный шкаф для своей коллекции книг.
I bought a bookcase for my book collection.
Here, 'книжный' modifies 'магазин', indicating that the store specializes in selling books.
В центре города есть книжный магазин.
There is a bookstore in the city center.
In this context, 'книжный' describes the style of writing as resembling or characteristic of books, possibly being formal or learned.