You can also use "Tatay" if you're referring to your father's father.
Here are some other words you can use depending on the context:
* Lolo/Lola: These words refer to both grandfather and grandmother.
* Ama/Ina: These words mean "father" and "mother" respectively. You can use them to refer to your grandfather and grandmother if you want to be more formal.
* Apó: This word is less common but can also be used to refer to a grandfather.
The best word to use will depend on the specific situation and your relationship with the person you are referring to.