Diamonds repeatedly cut into cubes (4)
I believe the answer is:
dice
'cut into cubes' is the definition.
(I've seen this before)
'diamonds repeatedly' is the wordplay.
'diamonds repeatedly' means two replacements for 'diamonds'.
'diamonds' becomes 'd' (abbreviation in bridge say).
'diamonds' becomes 'ice' (slang term for diamonds).
'd'+'ice'='DICE'
(Other definitions for dice that I've seen before include "Numbered cube(s)" , "Take a risk" , "Gamble; cut into cubes" , "Random number generators" , "Cut into small cubes" .)