Crossword Genius

Promoted I advanced avoiding acting like a mercenary? (9)

Ross

I believe the answer is:

soldierly

I'm a little stuck... Click here to teach me more about this clue!

'mercenary?' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I can't see?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in The Times and The Sunday Times.
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