Resentful, one's served up about six before us (7)
I believe the answer is:
envious
'resentful' is the definition.
(I've seen this before)
'one's served up about six before us' is the wordplay.
'served up' says the letters should be written backwards.
'about' is an insertion indicator.
'six' becomes 'vi' (roman numeral).
'before' means one lot of letters go next to another.
'one' in reverse letter order is 'eno'.
'eno' placed around 'vi' is 'envio'.
'envio'+'us'='ENVIOUS'
(Other definitions for envious that I've seen before include "resentful" , "Grudging of others" , "Feeling jealousy" , "Begrudging another's fortune" , "Green-eyed" .)