Gear about to go wrong (3)
I believe the answer is:
cog
'gear' is the definition.
(thesaurus)
'about to go wrong' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa'**).
'to' is a charade indicator (letters next to each other).
'wrong' is an anagram indicator.
'go' anagrammed gives 'og'.
'c'+'og'='COG'
(Other definitions for cog that I've seen before include "Minor person in organisation" , "minor employee" , "bar" , "Wheel with projections" , "One on a gearwheel" .)