Criminal greeting on card disheartened editor (8)
I believe the answer is:
hijacker
'criminal' is the definition.
(I know that hijacker is a type of criminal)
'greeting on card disheartened editor' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'on' means one lot of letters go next to another.
'card' becomes 'jack' (type of playing card).
'disheartened' says to hollow out the word (remove centre letters) (the middle or heart is removed).
'editor' with its middle removed is 'er'.
'hi'+'jack'+'er'='HIJACKER'
(Other definitions for hijacker that I've seen before include "Plane or ship seizer" , "One seizing control of plane" , "Seizer of vehicle controls" , "One who takes control of plane by force" , "one will divert passengers unexpectedly" .)