[Not my mistake] (3)
I believe the answer is:
sic
'not my mistake' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sic that I've seen before include "Word to call attention to a quoted mistake" , "As it stands, in printing" , "(Of quoted word) exactly so" , "Written exactly thus" , "Like" .)