Daily (3,4)
(Other definitions for per diem that I've seen before include "living expenses" , "For each day (Latin)" , "By the day, to the old Romans" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">daily</span>' is the definition.<br/ ><span class="explanation-format__explanation">(associated in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for diurnal that I've seen before include "Happening daily" , "in daylight" , "every day" , "Daily; during the daytime" , "Active during the day" .)