External form (5)
I believe the answer is:
shape
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">external form</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 shape that I've seen before include "Square, circle, etc." , "Phase (anag.)" , "'Figure, outline (5)'" , "Heaps (anag.)" , "Mould into new phase" .)