Diamonds sure to be frozen in (3-5)
(Other definitions for icebound that I've seen before include "Locked in by frozen water" , "Stuck in frozen water" , "(Arctic ship) stuck for winter" , "trapped by wintry conditions" , "Like ships trapped near poles" .)
'be frozen in' is the definition.
I know nothing about this answer so I can't judge whether this works.
'diamonds sure' is the wordplay.
'diamonds' becomes 'ice' (slang term for diamonds).
'sure' becomes 'bound' (synonyms).
'ice'+'bound'='ICE-BOUND'
'to' is the link.
Can you help me to learn more?
(Another definition for ice-bound that I've seen is " feeling the cold".)