Crossword Genius

One teacher is wrong (5)

Ross

I believe the answer is:

amiss

'is wrong' is the definition.
('amiss' can be a synonym of 'wrong')

'one teacher' is the wordplay.
'one' becomes 'a'.
'teacher' becomes 'miss' (I've seen this before).
'a'+'miss'='AMISS'

(Other definitions for amiss that I've seen before include "Wrong; inaccurate" , "error" , "Wrongly" , "In an inappropriate way" , "Faulty" .)

I've seen this clue in the Evening Standard.
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