The most common and most likely answer to this crossword clue is the 9 letter word BELLICOSE
I've seen this crossword clue in The Times
B
E
L
L
I
C
O
S
E
More clues leading to the result BELLICOSE
- Pugnacious bachelor taking girl round Greek island
- Militant ringer, one very big in church
- Contentious libel forced company to sack existing leaders
- Likely to be wielding weapon, one function to split peach
- Inclined to fight nasty libel case? Ring for answer
- Live with collie’s barking, becoming aggressive
- Aggressive corporation cut short one company’s enquiry, initially
- Aggressive black beagle finally upset collies
- Reportedly stomach companies becoming contentious
- Offensive ringer I nearly chose
Buddy explains!

The straight part
We know that "Militant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case militant = bellicose.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 BELLICOSE mean?
BELLICOSE adjective- Warlike in nature; aggressive; hostile.
- Showing or having the impulse to be combative.