Brightest star in the constellation Lyra (4)
I believe the answer is:
vega
'brightest star in the constellation 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 "First magnitude star" , "Gave turn to a star" , "heavenly body" , "Star in Lyra; grassy plain (Spanish)" , "Bright star of constellation Lyra" .)