Nucleus (4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nucleus</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for core that I've seen before include "essential element" , "Central or most important part of something" , "The centre of an object" , "The centre part, as of an apple" , "Centre, heart" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nucleus</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 kernel that I've seen before include "Edible seed of nut" , "Essential part" , "Inner part of nut" , "soft heart" , "Nut's centre" .)