Of three dimensions (5)
I believe the answer is:
cubic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of three dimensions</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cubic that I've seen before include "Like bones" , "Shaped like a solid square" , "Shaped like a die" , "Of the third power (mathematically)" , "The first C in cc" .)