/ˌʌndərˈmaɪn/
under·mine
BrE /ˌʌndəˈmaɪn/
NAmE /ˌʌndərˈmaɪn/
~ sth
to make sth, especially sb’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.
~ sth
to make sth weaker at the base, for example by digging under it