What word describes something that causes sleep?

The term "soporific" specifically refers to substances or activities that induce sleep or drowsiness. It originates from the Latin word "sopor," meaning deep sleep. A soporific effect can be commonly associated with certain medications, teas, or even environmental factors that promote relaxation and rest. In literature and conversation, describing something as soporific suggests that it has a calming, potentially sedating influence, making it a perfect fit for the definition of something that causes sleep.

The other options, while related to states of mind or physical states, do not align with the concept of causing sleep. For instance, stimulating refers to something that excites or energizes rather than relaxing someone to sleep. Inspirational evokes motivation or encouragement, which contrasts with the idea of prompting rest. Invigorating implies revitalization or increased energy, which again is the opposite of inducing sleep. Hence, "soporific" stands out as the correct choice, given its direct association with sleep induction.