Answer: undermine

AnswerCrossword Clue
UNDERMINESabotage
UNDERMINESap.
UNDERMINEWeaken
UNDERMINESap
UNDERMINEWeaken insidiously
undermineErode the base or foundation of (a rock formation)
undermineDamage or weaken (someone or something), esp. gradually or insidiously
undermineto dig beneath (eg a wall) in order to make it fall also UNDERMINDE
undermineDig or excavate beneath (a building or fortification) so as to make it collapse