Nagging (2,2)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nagging</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for persistent that I've seen before include "hanging on" , "Relentless" , "Tenacious; constant" , "Lasting, prolonged" , "Ongoing" .)