Synonyms for Posh:

adj.

elegant (adjective)
opulent, rich, deluxe.
expensive (adjective)
pricey.
fashionable (adjective)
trig, Tony, in.
luxurious, upper-class (adjective)
exclusive, opulent, chic, swanky, classy, trendy, fashionable, swish, modish, high-class, rich, swank, deluxe, ritzy, smart.
plush (adjective)
swanky.

n.

expensive, sumptuous, high-class, luxurious, costly, select, pricey, extravagant. chic, Tony, swank, in, trendy, smart, dashing, sharp, with-it, swanky, style, trig, snappy, modish, mod, usual. fancy, plain, exclusive, ritzy. posh (noun)
fashionable, stylish, classy, swish.

Other synonyms:

luxurious, mod, chic, trig, Tony. trendy, with-it, ritzy. modish, snappy, dashing. smart, in. sharp. restricted
exclusive.
sumptuous
rich.
Other relevant words:
high-class, trig, rich, select, chic, deluxe, swanky, fancy, luxurious, trendy, costly, Tony, plain, opulent, modish, snappy, smart, extravagant, in, pricey, with-it, exclusive, sharp, mod, ritzy, style, dashing, swank, usual, expensive, sumptuous.