Cerberus, say, pops up in Hades? (3)
I believe the answer is:
god
This clue could be a double definition.
'cerberus' is the first definition.
(thesaurus)
'hades?' is the second definition.
(hades is a kind of god)
'say pops up in' acts as a link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for god that I've seen before include "Anubis?" , "Being upstairs" , "Worshipped figure" , "Deity" , "eg Cupid" .)