1. Lacking in schooling
   "untaught people whose verbal skills are grossly deficient";
   - unschooled, untutored

1. Cause to disbelieve; teach someone the contrary of what he or she had learned earlier
   "The professor had to unteach some of the misconceptions the students had about physics"
    
2. Cause to unlearn
   "unteach somebody old habits or methods"

See also: uneducated

Type of: instruct, learn [archaic], teach