Formal:
* Akka (అక్క): This is the most common and respectful term for older sister.
* Chelli (చెల్లి): This is the respectful term for younger sister.
Informal:
* Anna (అన్న): Used by a younger sibling to address an older sister.
* Chelli (చెల్లి): This is used by an older sibling to address a younger sister.
Other:
* Sister (సిస్టర్): This is the English word used in some contexts.
Note: The choice of word also depends on the social setting and the speaker's age relative to the sister.