Star in the Summer Triangle (5)
I believe the answer is:
deneb
'star in the summer triangle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for deneb that I've seen before include "Bright star in Cygnus" , "The star Alpha Cygni" , "Be Ned (anag) - brightest star in Cygnus" , "Bright star; be end (anag.)" , "First magnitude star in Cygnus" .)