verb (used with object), un·der·mined, un·der·min·ing.
- to injure or destroy by insidious activity or imperceptible stages, sometimes tending toward a sudden dramatic effect.
- to attack by indirect, secret, or underhand means; attempt to subvert by stealth.
- to make an excavation under; dig or tunnel beneath, as a military stronghold.
- to weaken or cause to collapse by removing underlying support, as by digging away or eroding the foundation.
- (of the sea, wind, etc) to wear away the bottom or base of (land, cliffs, etc)
- to weaken gradually or insidiouslytheir insults undermined her confidence
- to tunnel or dig beneath
v.c.1300, undermyne, from under + mine (v.). The figurative sense is attested from early 15c. Cf. Dutch ondermijnen, Danish underminere, German unterminiren. Related: Undermined; undermining.