Diamonds - rocks (3)
I believe the answer is:
ice
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">diamonds</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(slang term for diamonds)</span><br/ ><br/ >'<span class="explanation-format__original">rocks</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(both can informally mean diamonds)</span><br/ ><br/ ></span>
(Other definitions for ice that I've seen before include "Decorate a cake" , "Cubes in a drink" , "Cool down" , "Do cake decoration" , "Formality" .)