Which term means causing sleep or something that induces sleep?

The term that refers to something that causes sleep or induces sleep is "soporific." This word originates from the Latin "sopor," meaning deep sleep, and it is commonly used in both medical and non-medical contexts to describe substances, such as certain medications or drugs, that can facilitate sleep. This term is particularly relevant when discussing pharmacology or treatments for insomnia, where the effects of soporific agents are intended to help individuals fall asleep more easily or improve sleep quality.

The other terms do not fit the definition of inducing sleep. For instance, "spurn" means to reject something disdainfully, "staunch" relates to being firm or steadfast, and "sluggard" describes a lazily inactive person, none of which pertain to the concept of inducing sleep. Hence, "soporific" is the accurate choice to describe something that brings about sleepiness.