Earl not about to sit on spades, say, in posh clothes (4,4)

'posh clothes' is the definition.

'earl not about to sit on spades say' is the wordplay.
'earl' becomes 'e'.
'about' is a reversal indicator.
'to sit on' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'spades say' becomes 'suit' (spades is an example of a card suit).
'not' written backwards gives 'ton'.
'e'+'ton'+'suit'='ETON SUIT'

'in' is the link.