- 1undermine something to make something, especially someone's confidence or authority, gradually weaker or less effective Our confidence in the team has been seriously undermined by their recent defeats. This crisis has undermined his position. Recent changes have undermined teachers' morale.
- 2undermine something to make something weaker at the base, for example by digging under it
NAmE//ˈʌndərˌmaɪn//, NAmE//ˌʌndərˈmaɪn//Verb Forms present simple I / you / we / they undermine
he / she / it undermines
past simple undermined
-ing form undermining