Which word means to undermine or take away the legal force of something?

The term "vitiate" specifically refers to the act of undermining or invalidating the legal force or efficacy of something. In legal contexts, to vitiate an agreement means to render it void or ineffective, often due to the presence of a flaw or defect. This term emphasizes the idea of corrupting or weakening something that is supposed to be strong or valid.

Other terms in the choices offered do not carry this specific legal connotation. "Propitiate" relates to appeasing or placating someone, often in a context of seeking favor or forgiveness. "Turgid" describes something that is swollen or inflated, frequently used in a metaphorical sense to critique language or writing that is pompous or overly ornate. "Wend" means to proceed in a specified direction or to follow a route. None of these alternatives convey the essential meaning of undermining legal validity that "vitiate" does, making it the clear and accurate choice in this context.