Undermine – English Flashcard for Undermine for IELTS Updated: August 12, 2019 by Dr. Mohammad Hossein Hariri AslUndermine Undermine (verb) /ˌʌn.dəˈmaɪn/ US /-dɚ-/to gradually make somebody or something less powerful, competent and effective – weaken:The point that he was interrupting me again and again was undermining my confidence.