This is the 5131st most frequent Catalan word.
arnau
"Arnau" is a Catalan male first name, equivalent to "Arnaud" or "Arnold" in English.
In this sentence, 'Arnau' is used as a proper noun, representing a person's name.
L'Arnau és un noi molt intel·ligent.
Arnau is a very intelligent boy.
Here, 'Arnau' again acts as a proper noun, indicating possession by the individual named Arnau.
Aquest llibre és d'Arnau.
This book belongs to Arnau.
'Arnau' functions as the subject of the sentence, denoting the person who will deliver the speech.