Not readily noticeable (13)
I believe the answer is:
inconspicuous
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not readily noticeable</span>' is the definition.<br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for inconspicuous that I've seen before include "Not prominent" , "Camouflaged" , "Attracting no attention" , "Unobtrusive" , "Undistinguished" .)