Basic constituent part (7)
I believe the answer is:
element
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">basic constituent part</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 element that I've seen before include "lead, for example" , "Fundamental component" , "part of cooker" , "Constituent part (7)" , "Operative part of an electric kettle" .)