* Atha (அத்தா): This is a common term used for grandfather, and it is the most similar word to "Thatha". It's generally used in a respectful and affectionate manner.
* Paatti (பாட்டி): While this means "grandmother," it is sometimes used as a term of endearment for grandfathers, especially by younger children.
* Tatta (தத்தா): This is another term for grandfather, but it's less common than "Thatha" and "Atha".
* Periyaappa (பெரியப்பா): This literally means "big father" and refers to an older male relative, including uncles and grandfathers.
* Vaera (வாற): This word is more formal and can be used to address an elderly male relative, including a grandfather, in a respectful manner.
The best word to use will depend on the speaker's relationship with the grandfather, the specific context, and the desired level of formality.