This is the 7114th most frequent Russian word.
большую
The Russian word "большую" means "big" or "large" in the feminine accusative singular form.
In this sentence, the word 'большую' is the accusative feminine singular form of the adjective 'большой', meaning 'big', qualifying the noun 'книга' (book) which is feminine.
Я купил большую книгу.
I bought a big book.
Here, 'большую' aligns with the feminine singular noun 'собака' (dog) in the accusative case, as it's the direct object of the action 'видела' (saw).
Она видела большую собаку в парке.
She saw a big dog in the park.
In this use, 'большую' modifies 'часть' (part), a feminine noun in accusative singular, to express a portion of a timeframe.