The dope under ground? (7)

I believe the answer is:

lowdown

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'the dope' is the definition.
(I've seen this before)

'under ground?' is the wordplay.
'under' becomes 'low' (similar in meaning).
'ground?' becomes 'down' (I can't explain this - if you can you should believe this answer much more).
'low'+'down'='LOWDOWN'

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(Other definitions for lowdown that I've seen before include "Data" , "Dope" , "confidential information" , "news" , "facts" .)

I've seen this clue in The Guardian.

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