Dearest father purchases cut diamonds (8)

'dearest' is the definition.
('pricy' can be a synonym of 'dear')

'father purchases cut diamonds' is the wordplay.
'father' becomes 'priest' (I've seen this in another clue).
'purchases' is an insertion indicator.
'cut' means to remove the last letter.
'diamonds' becomes 'ice' (slang term for diamonds).
'ice' with its last letter taken away is 'ic'.
'priest' enclosing 'ic' is 'PRICIEST'.