Silly fools (6)
I believe the answer is:
idiots
'silly fools' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for idiots that I've seen before include "Abusive word for unintelligent or irrational people" , "imbeciles" , "Nincompoops" , "Foolish ones" , "Silly fools" .)