Terribly posh store (4)
I believe the answer is:
shop
'store' is the definition.
(I know that shop is a class)
'terribly posh' is the wordplay.
'terribly' indicates anagramming the letters.
'posh' is an anagram of 'SHOP'.
(Other definitions for shop that I've seen before include "Retail premises" , "Retail outlet" , "Posh (anag.)" , "Store or boutique" , "Where goods are bought and sold" .)