Capitol is out of sight (7)
I believe the answer is:
optical
'of sight' is the definition.
(optical means relating to sight)
'capitol is out' is the wordplay.
'is out' indicates an anagram (I've seen 'was out' mean this).
'capitol' with letters rearranged gives 'OPTICAL'.
(Other definitions for optical that I've seen before include "Working with light" , "Using visible light" , "connected to light" , "Concerning sight" , "Capitol (anag.)" .)