unteach

verb

Etymology: From un- + teach.

1. To cause (someone) to unlearn; to make (someone) forget something they have been taught, or recognize it as erroneous, etc.

   “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, […]”

   “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. To cause (something previously learned) to be forgotten, or recognized as an error, etc.

   “"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.”

   “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.”