He's very stupid to continue (4)
I believe the answer is:
goon
'he's very stupid' is the definition.
(I've seen this before)
'to continue' is the wordplay.
'to' becomes 'go' (I am not sure about this - if you are sure you should believe this answer much more).
'continue' becomes 'on' (I've seen this in other clues).
'go'+'on'='GOON'
Can you help me to learn more?
(Other definitions for goon that I've seen before include "He's very stupid" , "Silly person - bully (US)" , "Foolish person - thug (US)" , "Sellers for example" , "Is this show" .)