Very old diamonds, say (5)
I believe the answer is:
Here is my best explanation:
'say' is the definition.
(voicing is a kind of saying)
'very old diamonds' is the subsidiary indication.
'very' becomes 'v' (abbreviation).
'old' becomes 'o'.
'diamonds' becomes 'ice' (I've seen this before).
(Other definitions for voice that I've seen before include "Express in words", "Wallop", "Sound with which one speaks", "Express, utter", "Utterance", "Power of speaking", "Speak of - mouthpiece", "Sound produced by humans", "Opinion; part in a fugue" and "Sound produced in speaking".)