Horrified sat, trembling, beside the awful hag (6)
I believe the answer is:
aghast
'horrified' is the definition.
(I've seen this in another clue)
'sat trembling beside the awful hag' is the wordplay.
'trembling' is an anagram indicator.
'beside' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the awful' indicates an anagram.
'sat' is an anagram of 'ast'.
'hag' with letters rearranged gives 'agh'.
'ast' put after 'agh' is 'AGHAST'.
(Other definitions for aghast that I've seen before include "Horrified, filled iwth consternation" , "'Appalled, dismayed (6)'" , "Filled with consternation or horror" , "Appalled, shocked" , "Thunderstruck" .)