Person with diamonds on upper part of dress (6)
I believe the answer is:
bodice
'upper part of dress' is the definition.
(I've seen this before)
'person with diamonds' is the wordplay.
'person' becomes 'bod' (I've seen this in other clues**).
'with' is a charade indicator (letters next to each other).
'diamonds' becomes 'ice' (I've seen this before).
'bod'+'ice'='BODICE'
'on' is the link.
(Other definitions for bodice that I've seen before include "Upperpart of woman's dress" , "Top half of a dress" , "Historical novel with lots of passion" , "Corset" , "which envelops the breast" .)