Grandfather in Austrian German translates to "Grossvater" but is also "Opa" which is more akin to "grandpa."
seanathair ANOTHER ANSWER: athair mór
The actual word is "Grandpère", however that means "Grandfather", and is fairly formal. Many French Canadians refer to their grandfathers as Pépère (pronounced sort of like pay-pear). There are...
Grootvader (formal) or Opa (informal).
Klasgenoot