Headless hag gets tons horror-stricken (6)
I believe the answer is:
aghast
'horror-stricken' is the definition.
(I know that horror-stricken can be written as aghast)
'headless hag gets tons' is the wordplay.
'headless' means to remove the first letter.
'gets' becomes 'has' ('have' can be a synonym of 'get').
'tons' becomes 't'.
'hag' with its first letter removed is 'ag'.
'ag'+'has'+'t'='AGHAST'
(Other definitions for aghast that I've seen before include "Stunned" , "Very unhappy" , "Shocked, dumbfounded" , "Taken aback with horror" , "in awe" .)