Napaceous is an unusual word meaning "drowsy or sleep-inducing." There are a few synonyms that can be used interchangeably to express the same sentiment. To describe a nap or sleep-inducing effect, words like soporific, hypnotic, lethargic, and somniferous are suitable. Another option could be to use more descriptive terms like calming, relaxing, soothing, or tranquilizing. These words can be used to describe the effect of certain activities or objects such as music, tea, or aromatherapy. Regardless of which word is used, it is important to choose one that best conveys the intended meaning and tone of the message.