Capitol out of sight (7)
I believe the answer is:
optical
'of sight' is the definition.
(optical means relating to sight)
'capitol out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'capitol' anagrammed gives 'OPTICAL'.
(Other definitions for optical that I've seen before include "some kind of illusion" , "Using visible light" , "Coal tip (anag)" , "Relating to the eye" , "Relating to vision and light" .)