"The furniture is big."
Translation:Os móveis são grandes.
(I may be wrong in this one)
I believe saying "a mobília é grande" means something different than saying "os móveis são grandes".
Mobília = furniture
Móvel = a piece of furniture
Móveis = plural of móvel. Can be interpreted as furniture in many cases.
But, correct me if I'm wrong, I believe big furniture means many pieces, not big pieces of furniture.
The English word "furniture" is singular (requires singular agreement), but can refer to "a" collection of things.
Portuguese has a word that refers to a single piece of furniture and can be made plural to refer to multiple pieces of furniture. Strange but.... Is "a mobilia" a collection of pieces of furniture? What is "as mobilias"?
Raf_iggy, furniture is used as both singular and plural. You seem to suggest there is no plural. https://englishgrammar.org/singular-plural-nouns/ "Some nouns have only a singular form or only a plural form. Nouns which have only a singular form include the following: furniture, wheat, happiness, scenery, news, information, luggage, bread..."