Lecturer caught finally in forbidden instruction (4)

I believe the answer is:

dont

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'forbidden instruction' is the definition.
The definition suggests a singular noun which matches the answer.

'lecturer caught finally' is the wordplay.
'lecturer' becomes 'don' (don can mean an academic).
'finally' indicates one should take the final letters.
The final letter of 'caught' is 't'.
'don'+'t'='DONT'

'in' is the link.

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I've seen this clue in The Guardian.

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