Not all reverential fear first is daunting (7)
I believe the answer is:
awesome
'is daunting' is the definition.
(I've seen this before)
'not all reverential fear first' is the wordplay.
'not all' becomes 'some' ('some' is the opposite to 'all').
'reverential fear' becomes 'awe' (I've seen this before).
'first' is a charade indicator (letters next to each other).
'some' put after 'awe' is 'AWESOME'.
(Other definitions for awesome that I've seen before include "Terrific" , "Mighty" , "Inspiring reverence mixed with fear" , "Generating fear and wonder" , "Amazing (sl.)" .)