Every seven days (6)
I believe the answer is:
weekly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">every seven days</span>' is the definition.<br/ ><span class="explanation-format__explanation">(happening every week)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for weekly that I've seen before include "magazine" , "Hebdomadal" , "eg Every Tuesday" , "Occurring every seven days" , "Periodical" .)