Mad sort of lament (6)

I believe the answer is:

mental

'mad' is the definition.
(thesaurus)

'sort of lament' is the wordplay.
'sort of' indicates an anagram.
'lament' is an anagram of 'MENTAL'.

(Other definitions for mental that I've seen before include "Nuts" , "Pertaining to the mind" , "Lament (anag) - of the mind" , "Involving the mind" , "off trolley" .)

I've seen this clue in The Daily Express and The Mirror.

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