Barrier; bird (4)
I believe the answer is:
rail
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">barrier</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(rail is a kind of barrier)</span><br/ ><br/ >'<span class="explanation-format__original">bird</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(a wading bird)</span><br/ ><br/ ></span>
(Other definitions for rail that I've seen before include "Part of train track" , "Waterside bird; part of track" , "Rant" , "Water bird; bar" , "Complain about - marsh bird" .)