Which term would best describe an object that is counterfeit?

The term that best describes an object that is counterfeit is "bogus." This word specifically refers to something that is fake or not genuine, which aligns perfectly with the concept of counterfeiting—where an object is made to imitate something of value but is actually a fraudulent version. In the context of items like currency, documents, or designer goods, calling an item "bogus" conveys that it lacks authenticity and is intended to deceive.

The other terms do not convey the same meaning. For instance, "genuine" and "legitimate" both suggest authenticity and are typically used to describe items that are real or accepted as valid. "Credible," on the other hand, relates to being believable or trustworthy, which does not apply to the nature of counterfeit objects. Therefore, "bogus" is the most appropriate descriptor for an object that is counterfeit.