This is the 1481st most frequent Portuguese word.
bonita
Beautiful.
In this sentence, 'bonito' is used to describe the aesthetic quality (beauty) of the smile.
Ela tem um sorriso muito bonito.
She has a very beautiful smile.
Here, 'bonita' is used to express the pleasing visual aspect of the landscape.
A paisagem aqui é tão bonita.
The landscape here is so beautiful.
In this instance, 'bonita' is applied figuratively, describing the admirable nature of the idea.