Placid artist turned up, showing original (7)
I believe the answer is:
radical
'original' is the definition.
(thesaurus)
'placid artist turned up showing' is the wordplay.
'showing' says the answer is hidden in the clue (the answer is shown in the clue).
'turned up' shows that the letters should be reversed in order.
'lacidar' can be found hidden inside 'placid artist'.
'lacidar' written backwards gives 'RADICAL'.
(Other definitions for radical that I've seen before include "One seeking root and branch reform" , "Militant" , "Complete" , "'Revolutionary, extremist (7)'" , "Of reform, fundamental and innovative" .)