Marshmallow spread (5)
I believe the answer is:
fluff
'marshmallow spread' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fluff that I've seen before include "Botch" , "Mistake; soft fibres" , "Light downy substance - mistake?" , "Make a mistake" , "Downy stuff; get (lines) wrong" .)