Garner’s Usage Tip of the Day recently had an interesting entry on near-synonyms for nouveau riche:
The gallicisms "parvenu" (/PAHR-vuh-noo/) and "arriviste" (/ah-ree-VEEST/) are synonymous, meaning "a person who is newly rich; an upstart." "Arriviste" can also refer to one who has recently acquired power or success that isn't necessarily monetary.
Garner also warns:
But "parvenu" and "arriviste" are uncommon enough that they smack of sesquipedality.
You can subscribe to Garner’s Usage Tip of the Day here.