Listener solver's rude (6)
I believe the answer is:
'rude' is the definition.
(earthy can mean rude or vulgar)
'listener solver's' is the wordplay.
'listener' becomes 'ear' (body part which hears or listens).
'solver's' becomes 'thy' (belonging to thee, the crossword solver).
(Other definitions for earthy that I've seen before include "Coarse, vulgar" , "Hearty (anag)" , "Gross, like the soil" , "Consisting of soil" , "Coarse as humour may be" .)