Disorganised; silly (14)
I believe the answer is:
scatterbrained
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">disorganised</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">silly</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for scatterbrained that I've seen before include "Inclined to forget" , "Unfocused" , "Disorganised, lacking concentration" , "absent-minded" , "easily distracted - with 20d" .)