Sweet deer, by the sound of it? (6)
I believe the answer is:
mousse
'sweet' is the definition.
(mousse is a kind of sweet)
'deer by the sound of it?' is the wordplay.
'deer' becomes 'moose' (moose is a kind of deer).
'by the sound of it?' shows a homophone (sound like).
'moose' sounds like 'MOUSSE'.
(Other definitions for mousse that I've seen before include "Frothy creamy substance for styling hair" , "F" , "hair product" , "A hair dressing; a creamy sweet" , "Shock treatment" .)