Brightest star in Lyra (4)
I believe the answer is:
vega
'brightest star in lyra' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vega that I've seen before include "Bright star of constellation Lyra" , "Fifth brightest star" , "heavenly body" , "Gave turn to a star" , "First magnitude star" .)