Crossword Genius

Teachers do it for money (4)

Ross

I believe the answer is:

mark

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'for money' is the definition.
(I have seen 'Old money' mean 'mark' so perhaps 'money' could also mean 'mark')

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for mark that I've seen before include "Take note of" , "The second Gospel" , "Brand - old German currency" , "Characteristic" , "Gospel writer" .)

I've seen this clue in The Irish News.
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