This is the 307th most frequent Croatian word.
novu
"Novu" means "new" in the feminine singular accusative form in Croatian.
In this sentence, 'novu' modifies 'knjigu' (book) and is used in the accusative singular feminine form as an adjective.
Kupio sam novu knjigu.
I bought a new book.
Here, 'novu' is in the accusative singular feminine form, describing the word 'haljinu' (dress), which is the object of the search.
Tražim novu haljinu za zabavu.
I am looking for a new dress for the party.
In this sentence, 'novu' is again in the accusative singular feminine form and modifies 'ideju' (idea), showing a qualitative attribute of the idea received.