Derision will dishearten a jester (4)
I believe the answer is:
jeer
'derision' is the definition.
(I know that jeer is a type of derision)
'dishearten a jester' is the wordplay.
'dishearten' says to hollow out the word (remove centre letters).
'jester' with its centre removed is 'JEER'.
'will' acts as a link.
(Other definitions for jeer that I've seen before include "Mock publicly" , "Rude, mocking remark" , "Laugh at with derision" , "Call out derisively" , "Mock rudely" .)