Every three months (9)
I believe the answer is:
quarterly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">every three months</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 quarterly that I've seen before include "Published every three months" , "Occurring every three months" , "Four times a year" .)