This is the 7483rd most frequent Portuguese word.
nadia
"Nadia" is not a Portuguese word; it is a name.
Here, 'Nádia' refers to a person's name, used as the subject of the sentence.
Nádia é uma excelente amiga que sempre está ao meu lado.
Nádia is an excellent friend who is always by my side.
In this sentence, 'Nádia' is used as a proper noun, indicating the person not seen.
Eu não vi Nádia na festa ontem à noite.
I did not see Nádia at the party last night.
Here, 'Nádia' shows possession, indicating the book belongs to Nádia.