Speak rudely to underworld god (3)
I believe the answer is:
dis
I believe this is a triple definition!
'speak rudely to' is the first definition.
(informal term meaning to disrespect)
'underworld' is the second definition.
(thesaurus)
'god' is the third definition.
(Dis is an example)
(Other definitions for dis that I've seen before include "Show contempt" , "Greek underworld" , "Roman god of the underworld" , "Treat without respect - god of the underworld" , "Name for Pluto or hell" .)