The most common and most likely answer to this crossword clue is the 8 letter word HIRELING
I've seen this crossword clue in Independent
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More clues leading to the result HIRELING
Buddy explains!
The straight part
We know that "mercenary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mercenary = hireling.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 HIRELING mean?
HIRELING noun- (usually derogatory) An employee who is hired, often to perform unpleasant tasks with little independence.
- (usually derogatory) Someone who does a job purely for money, rather than out of interest in the work itself.
- A horse for hire.
- A prostitute.