Extremist caught by powerful trap (5)
I believe the answer is:
ultra
'extremist' is the definition.
(ultra can mean an extremist or radical)
'caught by powerful trap' is the wordplay.
'caught by' says the answer is hidden in the clue.
'ULTRA' can be found hidden inside 'powerful trap'.
(Other definitions for ultra that I've seen before include "Above, beyond, super" , "Violet's predecessor" , "extreme measures" , "(One who is) extreme (in eg political opinion)" , "Prefix meaning excessively or extremely" .)