Formal:
* Achan: This is the most common and respectful way to address your grandfather. It literally translates to "father," but is used for elder males in general, including grandfathers.
* Appan: Another respectful term for grandfather, similar to "Achan."
* Thaatha: This is a more formal term for grandfather, often used by younger people.
Informal:
* Paapa: This is a familiar and affectionate term for grandfather, often used by grandchildren.
* Thatha: A more casual version of "Thaatha."
* Appu: This is a diminutive and affectionate term for grandfather, similar to "grandpa" in English.
Other options:
* Periyapappan: This literally means "big father" and is used for an elder paternal uncle, but can sometimes also be used for grandfather.
* Periyammappan: This literally means "big maternal uncle" and is used for an elder maternal uncle, but can sometimes also be used for grandfather.
The best way to address your grandfather is to ask your parents or other family members what they call him.