For father's side:
* Perummaa (പെരുമ്മാ): This is the most common and general term for grandaunt on the father's side.
* Achanthamma (അച്ഛന്തമ്മ): This refers specifically to the father's sister.
For mother's side:
* Ammaayi (അമ്മായി): This is the general term for grandaunt on the mother's side.
* Ammachi (അമ്മാച്ചി): This is a more affectionate term, often used for a grandmother or great-grandmother.
* Ammathumma (അമ്മത്തമ്മ): This refers specifically to the mother's sister.
Other possible terms:
* Muthassi (മുത്തശ്ശി): This is a general term for grandmother, and could be used for a grandaunt who is much older than you.
* Thatha (തത്ത): This is a general term for grandfather, and could be used for a grandaunt's husband.
The best word to use will depend on the specific context and the level of formality desired.