Female reproductive cell (4)
I believe the answer is:
ovum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">female reproductive cell</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 ovum that I've seen before include "A female egg-cell" , "Female gamete" , "Human egg cell" , "bit of life potentially" , "Female reproductive cell" .)