C'est une question d'accent ! Et pour les abréviations, je découvre la réponse de vinnycarbone sur https://forum.duolingo.com/comment/816575/av%C3%B3-e-av%C3%B4 : "In Brazil (at least) there are the short forms "vô" for "avô" (like the sound of "eau" in French) = grandfather and "vó" for "avó" (like "o" in "dog") = grandmother. However these short forms are informal. They are most commonly used in Portuguese spoken. P.S.: I'm a Brazilian. ;) "