Which term means to weaken or subvert in a deceptive manner?

The term that means to weaken or subvert in a deceptive manner is "undermine." This word specifically captures the essence of causing harm or damage in a discreet or subtle way, often without being immediately obvious. When one undermines something, they typically do so gradually, eroding its foundation or integrity. This might involve actions that seem harmless on the surface but ultimately lead to a deterioration of strength or effectiveness.

While "sabotage" also involves causing damage, it often implies a more overt and intentional disruption or obstruction of something. "Curtail" means to reduce or limit something, but it does not carry the connotation of deception. "Neglect" refers to failing to care for something adequately, which, while damaging, does not necessarily involve the stealthy undermining aspect that is central to the term "undermine."