Cast off; small building (4)
I believe the answer is:
shed
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cast off</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(shedding is a kind of casting off)</span><br/ ><br/ >'<span class="explanation-format__original">small building</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for shed that I've seen before include "Get rid of -- moult" , "storage unit" , "lost" , "place for bikes" , "Simple building; discard" .)