Horrified at hags dancing (6)
I believe the answer is:
aghast
'horrified' is the definition.
(thesaurus)
'at hags dancing' is the wordplay.
'dancing' is an anagram indicator.
'at'+'hags'='athags'
'athags' is an anagram of 'AGHAST'.
(Other definitions for aghast that I've seen before include "Filled with fear and consternation" , "Horrified, filled iwth consternation" , "Horror-stricken, filled with consternation" , "Deeply dismayed" , "Taken aback with horror" .)