Bird with a forked tail (4)
I believe the answer is:
tern
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bird with a forked tail</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tern that I've seen before include "Seagull" , "Gull-like seabird" , "Fork-tailed relative of the gull" , "Small gull with forked tail" , "Fork-tailed seabird" .)