Breathtaking sight (6)
I believe the answer is:
eyeful
'breathtaking sight' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eyeful that I've seen before include "One who is well worth looking at" , "A (lovely) sight to behold" , "Attractive sight" , "Gorgeous sight" , "someone beautiful" .)