Answer required for one in terrible challenge (4)
I believe the answer is:
dare
'terrible challenge' is the definition.
'dare' can be an answer for 'challenge' (dare is a kind of challenge). I am unsure of the 'terrible' bit.
'answer required for one in' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'required for one' becomes 'dre' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'a' inserted into 'dre' is 'DARE'.
Can you help me to learn more?
(Other definitions for dare that I've seen before include "Have sufficient courage" , "Risk; challenge" , "Have the courage to try something" , "Be bold enough (to)" , "Be courageous enough to try or do" .)