Trying again to pass engineers' session (9)

I believe the answer is:

resitting

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'trying again to pass' is the definition.
I can't tell whether this definition defines the answer.

'engineers' session' is the wordplay.
'engineers'' becomes 'RE' (abbreviation for Royal Engineers).
'session' becomes 'sitting' (sitting is a kind of session).
're'+'sitting'='RESITTING'

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I've seen this clue in The Daily Express.

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