1. To cause to forget or lose what has been taught.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• unreach,
• unteached,
• ynteach,
• hnteach,
• jnteach,
• inteach,
• 8nteach,
• 7nteach,
• ubteach,
• umteach,
• ujteach,
• uhteach,
• unfeach,
• ungeach,
• unyeach,
• un6each,
• un5each,
• untwach,
• untreach,
• unteacgh

• undeceive,
• undecagon,
• unattached,
• unhitch,
• untactful,
• unitize,
• undecided,
• unitise.

The adverb form of "unteach" is "unusually".