One sent on a mission devoid of ordinary jealousy (4)
I believe the answer is:
envy
'jealousy' is the definition.
(jealousy is an envious feeling)
'one sent on a mission devoid of ordinary' is the wordplay.
'one sent on a mission' becomes 'envoy' (I've seen this before).
'devoid of' indicates named letters should be taken away.
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'envoy' with 'o' taken away is 'ENVY'.
(Other definitions for envy that I've seen before include "Feeling of grudging admiration" , "One of the 7 deadly sins" , "Desire as a rival" , "grudge" , "Jealous emotion - deadly sin" .)