Simulant is a term used to describe an imitation, a replica or a substance that looks or behaves like another substance. Therefore, the antonyms of stimulant could be original, authentic, real, genuine or bona fide. These antonyms represent the opposite nature of simulant, as they are not intended to deceive or simulate a real thing, but rather they are genuine and true. For example, real diamonds are the antonym of simulant diamonds, as the former is made of actual carbon, while the latter is an imitation made of other materials. In short, antonyms of simulant are words that represent genuineness or truth, as opposed to imitation or deception.