Mush something to chew over (3)
I believe the answer is:
mug
'mush' is the definition.
(thesaurus)
'something to chew over' is the wordplay.
'something to chew' becomes 'gum' (I've seen this in another clue).
'over' shows that the letters should be reversed in order.
'gum' reversed gives 'MUG'.
(Other definitions for mug that I've seen before include "Gullible person" , "Drinking vessel, by gum" , "Vessel for a bit of a fool" , "Idiot" , "Tankard" .)