Which term best describes an act that is done deceitfully?

The term that best describes an act done deceitfully is "exploit." In this context, to exploit means to take advantage of someone or something, often in a deceptive manner. This aligns with the concept of deceit, as exploitation usually involves manipulation or unfair treatment to benefit oneself, typically at the expense of others.

The other terms have different meanings: "extinguish" refers to putting an end to something or causing it to cease altogether, "exuberant" describes a state of being filled with lively energy or excitement, and "falter" means to hesitate or waver in action or intent. None of these terms capture the essence of deceitful behavior in the way that "exploit" does.