Egg cell (4)
I believe the answer is:
ovum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">egg cell</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ovum that I've seen before include "bit of life potentially" , "Reproductive cell, 'egg' in Latin" , "Female gamete" , "Female reproductive cell" , "A female egg-cell" .)