Bad plonk, free (6)

I believe the answer is:

putrid

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'bad' is the definition.
(thesaurus)

'plonk free' is the wordplay.
'plonk' becomes 'put' (I can't justify this - if you can you should believe this answer much more).
'free' becomes 'rid' (to be free of something is to be rid of it).
'put'+'rid'='PUTRID'

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(Other definitions for putrid that I've seen before include "contaminated" , "Rotting, fetid" , "Decayed, rotten" , "Decomposing and fetid" , "Decomposed, rotting" .)

I've seen this clue in The Times.

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