Piece of crockery on a posh table (7)
I believe the answer is:
plateau
'table' is the definition.
(I've seen this before)
'piece of crockery on a posh' is the wordplay.
'piece of crockery' becomes 'plate' (plate is a piece of crockery).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'plate'+'a'+'u'='PLATEAU'
(Other definitions for plateau that I've seen before include "High, level tract of land" , "somewhere flatter?" , "High plain" , "High level land area" , "level part of range" .)