Informal (6)
I believe the answer is:
casual
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">informal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for casual that I've seen before include "Free-and-easy" , "Occasional worker" , "Irregular" , "Without formality" , "Informal or happening by chance" .)