This is the 8000th most frequent Polish word.
największy
"Największy" means "the biggest" or "the greatest."
This sentence uses 'największy' to compare a city in terms of size and importance, making it a superlative adjective.
Warszawa jest największym miastem w Polsce.
Warsaw is the biggest city in Poland.
Here, 'największy' describes the intensity or significance of a problem, also as a superlative adjective.
Największym problemem w tym projekcie była jego realizacja.
The biggest problem in this project was its implementation.
In this case, 'największy' is used to emphasize the extent or magnitude of the selection of books, again functioning as a superlative adjective.