The most common and most likely answer to this crossword clue is the 4 letter word SATI
S
A
T
I
Buddy explains!
The straight part
We know that "old Indian practice" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old indian practice = sati.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SATI mean?
SATI noun- The traditional custom of a Hindu woman giving herself up to be cremated on her husband’s funeral pyre as a sign of her devotion.