Form of flattery originally praising peer’s jewellery (9,6)
I believe the answer is:
imitation pearls
'jewellery' is the definition.
(I have seen 'Fake jewellery ' mean 'imitation pearls' so perhaps 'jewellery' could also mean 'imitation pearls')
'form of flattery originally praising peer's' is the wordplay.
'form of flattery' becomes 'imitation' ('imitation is the sincerest form of flattery').
'originally' says to take the initial letters.
'peer's' becomes 'earls' (earl is a kind of peer).
The first letter of 'praising' is 'p'.
'imitation'+'p'+'earls'='IMITATION PEARLS'
(Another definition for imitation pearls that I've seen is " Fake jewellery".)