Extremist engaged in awful trade (5)
I believe the answer is:
ultra
'extremist' is the definition.
('ultra' can be a synonym of 'extremist')
'engaged in awful trade' is the wordplay.
'engaged in' says the answer is hidden in the clue.
'ULTRA' can be found hidden inside 'awful trade'.
(Other definitions for ultra that I've seen before include "Far beyond the norm" , "(One who is) extreme (in eg political opinion)" , "Prefix meaning extreme or excessive" , "Over the top" , "Political extremist" .)