This is the 3815th most frequent Portuguese word.
castanho
Brown.
In this sentence, 'castanho' is used as an adjective to describe a color (brown).
O meu cabelo é castanho.
My hair is brown.
Here, 'castanho' serves as a noun referring to a horse of the color brown.
Eu vi um castanho no campo.
I saw a brown horse in the field.
'Castanhos' is used as an adjective to describe the color of the shoes.