This is the 1938th most frequent German word.
breit
Wide; broad.
Here, 'breit' is used as an adjective to describe the width of the street.
Die Straße ist sehr breit.
The street is very broad.
In this context, 'breit' is used figuratively to describe the expressiveness of the smile.
Er hat ein breites Lächeln im Gesicht.
He has a broad smile on his face.
'Breit' acts as an attribute to the noun 'Fluss', indicating its width.