The most common and most likely answer to this crossword clue is the 12 letter word SMALL-MINDED
S
M
A
L
L
-
M
I
N
D
E
D
Buddy explains!
The straight part
We know that "Petty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case petty = small-minded.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 SMALL-MINDED mean?
SMALL-MINDED adjective- Selfish, petty; constrained in thought, limited in scope of consideration, not mindful of the big picture.