Diamonds, geometrically (6)
I believe the answer is:
rhombi
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">diamonds geometrically</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rhombi that I've seen before include "Diamond shapes (maths.)" , "diamonds" , "certain figures in mathematics" , "Four-sided figures" , "Forms of parallelograms" .)