Bell possibly attached to head of awful monster (7)
I believe the answer is:
chimera
'monster' is the definition.
(I know that Chimera is a type of mythical creature)
'bell possibly attached to head of awful' is the wordplay.
'bell possibly' becomes 'chimer' (bells are things which chime).
'attached to' means one lot of letters go next to another.
'head of' says to take the initial letters.
The initial letter of 'awful' is 'a'.
'chimer'+'a'='CHIMERA'
(Other definitions for chimera that I've seen before include "Illusion" , "fake image" , "Chair me to find mixed monster of Greek myth" , "Mythological animal; something illusory" , "phantom" .)