Which term is the opposite of assist or help?

The term that is the opposite of assist or help is "undermine." When you assist or help someone, you are providing support or making their situation better. In contrast, to undermine means to weaken or damage someone’s ability to achieve their goals or to make a situation more difficult for them. It implies a negative action, where instead of providing aid, one is covertly or indirectly causing harm or hindrance to another's abilities or efforts.

The other terms listed—assist, support, and facilitate—all convey the idea of providing help or making a process easier, which aligns with the concept of assistance rather than opposition.