Radical people on reflection embracing calm (6)
I believe the answer is:
placid
'calm' is the definition.
(similar in meaning)
'radical people on reflection embracing' is the wordplay.
'embracing' says the answer is hidden in the clue (the solution is embraced by words in the clue).
'on reflection' says the letters should be written backwards.
'dicalp' is hidden within 'radical people'.
'dicalp' reversed gives 'PLACID'.
(Other definitions for placid that I've seen before include "Composed or serene" , "Unexcitable" , "Calm, phlegmatic" , "Collected" , "Serene - unruffled" .)