This is the 12770th most frequent Spanish word.
olvidado
Forgotten.
Here, 'olvidado' acts as an adjective, describing the noun 'libro' while retaining its origin from the verb 'olvidar.'
El libro olvidado en el aula era muy importante.
The book forgotten in the classroom was very important.
In this sentence, 'olvidado' functions as a past participle in a passive voice construction, indicating that the action of forgetting was done by an undefined subject.
Ese proyecto parece haber sido olvidado por todos.
That project seems to have been forgotten by everyone.
Here, 'olvidado' is used as the past participle of the verb 'olvidar,' forming a perfect tense.