Periodic (12)
I believe the answer is:
intermittent
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">periodic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for intermittent that I've seen before include "Occasional" , "On-and-off" , "Occurring irregularly" , "Not continuous or steady" , "Irregular" .)