Hero disheartened by a kiss prank (4)
I believe the answer is:
hoax
'prank' is the definition.
(I've seen this before)
'hero disheartened by a kiss' is the wordplay.
'disheartened' says to hollow out the word (remove centre letters).
'by' says to put letters next to each other.
'kiss' becomes 'x' (X can represent a kiss).
'hero' with its middle removed is 'ho'.
'ho'+'a'+'x'='HOAX'
(Other definitions for hoax that I've seen before include "A plan to deceive" , "Kid" , "Scam" , "Practical joke" , "Leg-pull" .)