This is the 3318th most frequent French word.
valu
"Valu" is not a standard French word. It may be a misspelling or informal usage.
In this sentence, the word 'valu' is used as the past participle of the verb 'valoir', meaning 'to be worth', addressing the value of a painting in a monetary sense.
Il a valu beaucoup d'argent pour ce tableau.
It was worth a lot of money for this painting.
Here, 'valu' conveys that the watch justified the wait, extending its use as 'to be worth' conceptually rather than monetarily.
Cette montre a valu la peine d'attendre.
This watch was worth waiting for.
In this instance, 'valu' indicates that the old book caused or earned an effect (worldwide fame), demonstrating broader applications of the verb 'valoir'.