Breakdown of O meu livro velho está sujo.
o livro
the book
estar
to be (temporary / location)
meu
my (m/f/pl: meu, minha, meus, minhas)
velho
old
Questions & Answers about O meu livro velho está sujo.
Why is there an O at the beginning of the sentence? Doesn't meu livro already mean "my book"?
Yes, but in European Portuguese, it is a standard rule to put a definite article (o or a, meaning "the") before a possessive word. So you literally say "The my book" (O meu livro).
Why is it livro velho instead of velho livro?
In Portuguese, descriptive adjectives like velho (old) almost always come after the noun they describe. So, instead of the English order "old book", you use the order "book old" (livro velho).
Notice how almost every word ends in -o? Is that a coincidence?
Not at all! This is gender agreement in action. Because the main noun livro (book) is masculine and singular, all the words connected to it must match. The article (o), possessive (meu), and both adjectives (velho and sujo) take their masculine singular forms.
Why does the sentence use está for "is" instead of é?