Five-sided shape (8)
I believe the answer is:
pentagon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">five-sided shape</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 pentagon that I've seen before include "military building" , "rectangle snipped at one corner?" , "Headquarters of the US Defence Department" , "US government building" , "Five-sided shape" .)