Formal:
* அக்கா (akka): This is the most common and general term for an older sister.
* தங்கை (thangai): This is the most common and general term for a younger sister.
* சகோதரி (sakodari): This is a more formal and literary term for a sister, used in writing and sometimes in formal speech.
Informal:
* அக்கா (akka): Can also be used informally for an older sister, even if the speaker is older.
* தங்கை (thangai): Can also be used informally for a younger sister, even if the speaker is younger.
* சகோ (sago): A more familiar and casual term for a sister, used by siblings and close friends.
Other:
* அண்ணி (anni): This term refers to a brother's wife (sister-in-law).
* மாமா (mama): This term refers to a sister's husband (brother-in-law).
The best translation will depend on the specific situation and the relationship between the speakers.