Star in Cygnus
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">star in cygnus</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 deneb that I've seen before include "First magnitude star in Cygnus" , "Be Ned (anag) - brightest star in Cygnus" , "Bright star in Cygnus" , "Bright star; be end (anag.)" , "The star Alpha Cygni" .)