The most common and most likely answer to this crossword clue is the 9 letter word ARMOURIES
I've seen this crossword clue in Financial Times
A
R
M
O
U
R
I
E
S
More clues leading to the result ARMOURIES
Buddy explains!
The straight part
We know that "They supply" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they supply = armouries.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 ARMOURIES mean?
ARMOURIES noun- Heraldry
- A place where arms are kept, an arsenal.
- A collection of weapons and materiel.
- A place where arms are made.