One who doesn't believe that he is taking part (7)
I believe the answer is:
atheist
'one who doesn't believe that he is taking part' is the definition.
'atheist' can be an answer for 'one who doesn't believe'. I'm not sure about the rest of the definition.
'believe that he is taking part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'ATHEIST' can be found hidden inside 'believe that he is taking'.
Can you help me to learn more?
(Other definitions for atheist that I've seen before include "One who does not believe in the existence of a god" , "One doesn't believe" , "One who disbelieves the existence of gods" , "One who believes there is no god" , "Person who does not believe in existence of a god" .)