This is the 11th most frequent Vietnamese word.
nhiều
"Many" or "much."
Here, 'nhiều' functions as an adjective modifying the noun 'sách', indicating quantity.
Tôi có nhiều sách trong thư viện.
I have many books in the library.
In this sentence, 'nhiều' acts as an adverb to compare quantity in the phrase 'ăn nhiều hơn'.
Cô ấy ăn nhiều hơn tôi.
She eats more than I do.
'Nhiều' is used as an adjective to indicate the abundance of 'điều thú vị' (interesting things).