The most common and most likely answer to this crossword clue is the 9 letter word COLUMBINE
I've seen this crossword clue in The Times
C
O
L
U
M
B
I
N
E
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The straight part
We know that "Panto character once" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case panto character once = columbine.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 COLUMBINE mean?
COLUMBINE noun- Any plant of the genus Aquilegia, having distinctive bell-shaped flowers with spurs on each petal.
- Pertaining to a dove or pigeon.