Distinguished relative with diamonds (5)
I believe the answer is:
grand
'distinguished' is the definition.
(I know that distinguished can be written as grand)
'relative with diamonds' is the wordplay.
'relative' becomes 'gran' (short for grandmother).
'with' is a charade indicator (letters next to each other).
'diamonds' becomes 'd' (abbreviation in card games).
'gran'+'d'='GRAND'
(Other definitions for grand that I've seen before include "principal" , "Piano; thousand pounds" , "pair of monkeys?" , "Magnificent, imposing" , "One thousand pounds" .)