Rodent devouring singular dessert (6)
I believe the answer is:
mousse
'dessert' is the definition.
(mousse is a kind of dessert)
'rodent devouring singular' is the wordplay.
'rodent' becomes 'mouse' (mouse is a kind of rodent).
'devouring' is an insertion indicator.
'singular' becomes 's' (abbreviation in grammar).
'mouse' going around 's' is 'MOUSSE'.
(Other definitions for mousse that I've seen before include "Gel" , "Pope's representative" , "Whipped savoury dish" , "cold dish" , "A hair dressing; a creamy sweet" .)