Outright source of hope in prophet (5)
I believe the answer is:
sheer
'outright' is the definition.
(thesaurus)
'source of hope in prophet' is the wordplay.
'source of' suggests taking the first letters.
'in' indicates putting letters inside.
'prophet' becomes 'seer' (I've seen this before).
The first letter of 'hope' is 'h'.
'h' put inside 'seer' is 'SHEER'.
(Other definitions for sheer that I've seen before include "Very fine like silk stockings" , "avoid an unpleasant thing" , "Completely" , "Precipitous or fine" , "Film" .)