What’s just sweet to the ear? (6)
I believe the answer is:
desert
'what's just' is the definition.
(as in 'just deserts', that which is fair or just)
'sweet to the ear?' is the wordplay.
'sweet' becomes 'dessert' (synonyms).
'to the ear?' shows a homophone (sound like) (I've seen 'to the ear' mean this).
'dessert' sounds like 'DESERT'.
(Other definitions for desert that I've seen before include "Abandon in wasteland" , "infertile land" , "sands" , "Run away (from army)" , "Abandon in arid area" .)