The most common and most likely answer to this crossword clue is the 13 letter word TRIGGER-HAPPY
I've seen this crossword clue in Financial Times
T
R
I
G
G
E
R
-
H
A
P
P
Y
Buddy explains!
The straight part
We know that "bellicose" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bellicose = trigger-happy.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 TRIGGER-HAPPY mean?
TRIGGER-HAPPY adjective- Having a tendency or desire to shoot a firearm irresponsibly before adequately identifying the target.
- (by extension) Inclined to behave recklessly or violently at the slightest provocation.