Large heavy bird (7)
I believe the answer is:
bustard
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large heavy bird</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for bustard that I've seen before include "Long-legged, heavy-bodied bird" , "See large bird" , "Bad rust (anag.)" , "flyer" , "Large heavy bird" .)