This is the 5946th most frequent Portuguese word.
bons
"Good" (plural, masculine).
In this sentence, "bons" describes "amigos", indicating their good or desirable quality.
Bons amigos sempre apoiam uns aos outros.
Good friends always support each other.
Here, "bons" modifies "livros", specifying their suitability or quality for the purpose mentioned.
Aqueles livros são tão bons para aprender sobre história.
Those books are so good for learning about history.
In this sentence, "bons" relates to "exercícios físicos", expressing their beneficial effect towards health.