The most common and most likely answer to this crossword clue is the 5 letter word NORMA
I've seen this crossword clue in The Times
N
O
R
M
A
More clues leading to the result NORMA
- Female occupying barn or mansion
- Line cut from standard opera
- Finish off standard musical work
- Sexy Marilyn's short routine
- Female — with and without male
- Opera stars
- Heroine doomed to die, and not an old lady
- High priestess and not mother
- Bellini's heroine, not quite orthodox
- Opera singer Jessye, without second name?
Buddy explains!

The straight part
We know that "High priestess" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case high priestess = norma.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.