Cop it accidentally in the eye (5)
I believe the answer is:
optic
'the eye' is the definition.
(synonyms)
'cop it accidentally' is the wordplay.
'accidentally' is an anagram indicator (a chaotic or accidental ordering of the letters).
'cop'+'it'='copit'
'copit' is an anagram of 'OPTIC'.
'in' acts as a link.
(Other definitions for optic that I've seen before include "Describing a sensory organ" , "Relating to sight" , "Device for measuring out spirits" , "Body part" , "Pertaining to sight" .)