Spot a misplaced bolt (4)
I believe the answer is:
blot
'spot' is the definition.
(synonyms)
'a misplaced bolt' is the wordplay.
'a misplaced' is an anagram indicator (letters in the wrong places).
'bolt' anagrammed gives 'BLOT'.
(Other definitions for blot that I've seen before include "stain on reputation" , "Smudge (on escutcheon?)" , "Soak up (ink); blemish" , "Smudge of ink" , "Stain left by spilled ink" .)