The most common and most likely answer to this crossword clue is the 6 plus 3 letter word BATTLE AXE
I've seen this crossword clue in Financial Times
B
A
T
T
L
E
A
X
E
Buddy explains!
The straight part
We know that "bill" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bill = battle axe.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 BATTLE AXE mean?
BATTLE AXE noun- An ancient military weapon, an axe designed for combat.
- This weapon borne on arms as a mark of prowess.
- A domineering, antagonistic woman.
- An electric guitar.
- (usually spelt "battleaxe") An allotment of land at the rear of another property, with a long, narrow strip of land connecting it to the roadway.