Picnic hamperer (4)
I believe the answer is:
rain
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">picnic hamperer</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rain that I've seen before include "Falling water" , "Fall in large quantities" , "See 12" , "Cats and dogs?" , "eg A shower" .)