Type of polyhedron (7)
I believe the answer is:
pyramid
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">type of polyhedron</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pyramid that I've seen before include "Ancient Egyptian building" , "Shape with square base and four triangular sides" , "Object with polygonal base and triangular sides meeting at point" , "A 3D shape" , "Massive Egyptian memorial" .)