When looking for synonyms for the word "sleepinducer," there are a few options to consider. "Soporific" is a commonly used term that denotes something that causes sleepiness or drowsiness. "Hypnotic" is another term that connotes inducing sleep, often used in the field of medicine. "Sedative" is a more general term that refers to anything that has a calming or tranquilizing effect, which can include inducing sleep. "Tranquilizer" is another synonym that can be used to describe a sleepinducer, often used to describe medications or substances that have a calming effect on the body. Overall, there are several synonyms available to describe something that induces sleep, each with slightly different nuances and connotations.