Much smashed to pieces in the underworld! (5)
I believe the answer is:
hades
'underworld' is the definition.
(Hades can mean the underworld in Greek myth)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for hades that I've seen before include "The underworld where the souls of the dead live" , "Greek underworld with spirits of the dead" , "It's hell in the Greek shade" , "Infernal situation" , "In Greek myth, the Underworld" .)