Cut off silly person (5)
I believe the answer is:
prune
This clue is a double definition.
'cut off' is the first definition.
(thesaurus)
'silly person' is the second definition.
(Other definitions for prune that I've seen before include "Trim (tree); dried plum" , "Dull person" , "Trim - dried fruit" , "Shrivelled fruit" , "Cut back the dried plum" .)