Tell lies about retired copper blocking deal (7)
I believe the answer is:
traduce
'tell lies about' is the definition.
(I've seen this before)
'retired copper blocking deal' is the wordplay.
'retired' is a reversal indicator.
'copper' becomes 'cu' (chemical symbol).
'blocking' is an insertion indicator.
'deal' becomes 'trade' ('trade' can be a synonym of 'deal'**).
'cu' written backwards gives 'uc'.
'uc' put into 'trade' is 'TRADUCE'.
(Other definitions for traduce that I've seen before include "Calumniate" , "Misrepresent in unfavourable way" , "Speak ill of" , "Speak badly of" , "Defame, slander" .)