Petty scam disheartened everyone (5)
I believe the answer is:
small
'petty' is the definition.
(synonyms)
'scam disheartened everyone' is the wordplay.
'disheartened' says to hollow out the word (remove centre letters).
'everyone' becomes 'all' (all people).
'scam' with its middle taken out is 'sm'.
'sm'+'all'='SMALL'
(Other definitions for small that I've seen before include "Lower middle of the back" , "Of no great size" , "Piddling" , "Young; modest" , "Social chat" .)