The most common and most likely answer to this crossword clue is the 10 letter word ETHERISING
I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Employing number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case employing number = etherising.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 ETHERISING mean?
ETHERISING verb- To convert into ether.
- To render insensible by means of ether, as by inhalation.