The most common and most likely answer to this crossword clue is the 13 letter word COMMISSIONING
I've seen this crossword clue in The Daily Telegraph
C
O
M
M
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S
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Buddy explains!
The straight part
We know that "Appointing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case appointing = commissioning.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 COMMISSIONING mean?
COMMISSIONING verb- To send or officially charge someone or some group to do something.
- To place an order for (often piece of art)
- To put into active service
- The process of assuring that all systems and components of a major piece of equipment, a process, a building or similar are designed, installed and tested according to the operational requirements of the owner or final client.