Pius etc must keep holy symbols of remembrance (7)
I believe the answer is:
poppies
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">symbols of remembrance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(Remembrance Day poppies)</span><br/ ><br/ >'<span class="explanation-format__original">pius etc must keep holy</span>' is the wordplay.<br/ >'<span class="explanation-format__original">pius etc</span>' becomes '<span class="explanation-format__intermediate">popes</span>' <span class="explanation-format__explanation">(several popes have been called Pius)</span>.<br/ >'<span class="explanation-format__original">must keep</span>' means one lot of letters goes inside another.<br/ >'<span class="explanation-format__original">holy</span>' becomes '<span class="explanation-format__intermediate">pi</span>' <span class="explanation-format__explanation">(pi can mean pious)</span>.<br/ >'<span class="explanation-format__intermediate">popes</span>' going around '<span class="explanation-format__intermediate">pi</span>' is '<span class="explanation-format__answer">POPPIES</span>'.<br/ ></span>
(Other definitions for poppies that I've seen before include "Scarlet flowers" , "Large bright flowers" , "Opium-yielding flower plants" , "Sources of opium" .)