This is the 14211th most frequent Spanish word.
trescientos
Three hundred.
Here, 'trescientos' is used as a numerical adjective quantifying the noun 'libros' (books).
Hay trescientos libros en la biblioteca.
There are three hundred books in the library.
'Trescientos' functions as part of a number in monetary value, modifying 'pesos' (currency).
Compré una chaqueta por trescientos pesos.
I bought a jacket for three hundred pesos.
In this context, 'trescientos' quantifies the unit 'degrees', referring to temperature.