Happy beginning for parvenu (7)
I believe the answer is:
upstart
'for parvenu' is the definition.
(synonyms)
'happy beginning' is the wordplay.
'happy' becomes 'up' (I've seen this in other clues).
'beginning' becomes 'start' (synonyms).
'up'+'start'='UPSTART'
(Other definitions for upstart that I've seen before include "Tap rust (anag.)" , "Arriviste, parvenu" , "Bumptious parvenu" , "One who has risen suddenly to high position, and is arrogant with it" , "Person who has suddenly risen in wealth or importance" .)