The most common and most likely answer to this crossword clue is the 7 plus 2 plus 3 plus 5 letter word PELICAN IN HER PIETY
I've seen this crossword clue in The Times
P
E
L
I
C
A
N
I
N
H
E
R
P
I
E
T
Y
Buddy explains!
The straight part
We know that "Heraldic feature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heraldic feature = pelican in her piety.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.