One suffering for their beliefs (6)
I believe the answer is:
martyr
'one suffering for their beliefs' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for martyr that I've seen before include "One who suffers for beliefs" , "One suffers for the sake of principle" , "put at stake?" , "One suffering or dying for a cause" , "One killed for cause" .)