American ostrich (4)
I believe the answer is:
rhea
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">american ostrich</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 rhea that I've seen before include "Big bird" , "Large S. American bird" , "Moon" , "New World flightless bird" , "It can't fly" .)