sundae topper (6)
I believe the answer is:
cherry
'sundae topper' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cherry that I've seen before include "Tree with stoned fruit" , "new ball?" , "Deep red like small round fruit" , "Small red stone-fruit from tree" , "Morello-flavoured liqueur" .)