Very bright star (4)
I believe the answer is:
nova
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">very bright star</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nova that I've seen before include "Star briefly brightening" , "Star that suddenly increases in brightness" , "Exploding star" , "Star that becomes much brighter for short time" , "Star showing a sudden, brief increase in luminosity" .)