90-degree angles (4)
I believe the answer is:
ells
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">90-degree angles</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 ells that I've seen before include "Old yards" , "Lengths of cloth" , "Former length measures" , "Extensions at right angles to the main building" , "Cloth measures" .)