Formal:
* दादा (Dada): This is the most common and formal way to refer to a grandfather.
Informal:
* नाना (Nana): This is used for a grandfather on the mother's side.
* दादाजी (Dada ji): This is a more respectful and endearing way to address a grandfather.
* बापू (Bapu): This is a more affectionate and informal term, similar to "grandpa" in English.
Other options:
* परदादा (Par Dada): This means great-grandfather.
* ननिहाल (Nanhihal): This refers to the maternal grandfather's family.
* नानाजी (Nana ji): This is a more respectful and formal way to refer to a maternal grandfather.
The best way to choose the right term depends on the specific situation and the relationship you have with the person.