Hors d'oeuvre -- it's eaten by vulgar son (8)
I believe the answer is:
crudites
'hors d'oeuvre' is the definition.
(crudites are served as hors d'oeuvre)
'it's eaten by vulgar son' is the wordplay.
'eaten by' means one lot of letters goes inside another.
'vulgar' becomes 'crude' (synonyms).
'son' becomes 's' (genealogical abbreviation for son).
'it' going inside 'crude' is 'crudite'.
'crudite'+'s'='CRUDITES'
(Other definitions for crudites that I've seen before include "Nibbles" , "Sliced vegetables" , "Raw vegetables served with a dip" , "Mixed raw vegetables served as an hors d'oeuvre" .)