Derived perhaps from the Latin pilus pili, hair. In Alistano and also in Miranda do Douro and other areas of Tras-os-Montes, a little bird that has just hatched and has hair instead of feathers. The Allista raptors used to say that the piluetros had donkey's hair. Their appearance of nakedness gave rise to the expression "ir a piluetro", to go naked
