unteach

From un- +‎ teach.

unteach (third-person singular simple present unteaches, present participle unteaching, simple past and past participle untaught)

1. (transitive) To cause (someone) to unlearn; to make (someone) forget something they have been taught, or recognize it as erroneous, etc.
   • 1846, Thomas Cooper, Two Orations Against Taking Away Human Life Under Any Circumstances: And in Explanation, and Defence of the Misrepresented Doctrine of Non-resistance ..., page 23:

     The heart of man has been long mistaught, and, I fear, it will require something that shall come closer home than legal enactments to unteach it. And nothing but example can teach it anew. It will never learn to love instead of to hate, […]

   • 1872, The Southern Magazine, page 324:

     It is difficult enough, when a pupil has been taught wrong in books, to unteach him and to set his mind going upon some reasonable plan; but to undertake to teach those who, though they have been to school, […]

2. (transitive) To cause (something previously learned) to be forgotten, or recognized as an error, etc.
   • 1859, The Christian Observer, page 603:

     "I did say that the mass was the Romish name for the sacrament." Upon which the rector "beat his head like a man distracted;" and declared that he should into the school and unteach that also.

   • 2014, Jeremy Bentham, The Book of Fallacies, Oxford University Press, USA, →ISBN, page 316:

     The great difficulty, and surely no small honour, is, or would be, to unlearn it: in the case of this as of so many other fallacies, by teaching it, the humble endeavour here is to unteach it.

• Cauthen, Chanute