Coal pit is moved out of sight (7)
I believe the answer is:
optical
'of sight' is the definition.
(optical means relating to sight)
'coal pit is moved' is the wordplay.
'is moved' indicates anagramming the letters.
'coal'+'pit'='coalpit'
'coalpit' with letters rearranged gives 'OPTICAL'.
'out' acts as a link.
(Other definitions for optical that I've seen before include "Involving light" , "Concerning light" , "Capitol (anag.)" , "Topical (anag.)" , "Visual" .)