In the wrong (2,5)
'in the wrong' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mistaken that I've seen before include "Wrong in opinion, judgment etc." , "'Wrong, misguided (8)'" , "In error in mankiest way" , "Wrongly understood" , "Wrong-headed" .)
'in the wrong' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for at fault that I've seen before include "Rightly taking the blame" , "In the wrong" , "Guilty" , "To blame, culpable" , "To blame, responsible for mistake" .)