Fifth-brightest star in the night sky (4)
I believe the answer is:
vega
'fifth-brightest star in the night sky' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for vega that I've seen before include "First magnitude star" , "Star in Lyra; grassy plain (Spanish)" , "Bright star of constellation Lyra" , "Brightest star of constellation Lyra" , "Gave turn to a star" .)