Which word refers to something that provides relief from pain?

The term that refers to something that provides relief from pain is "anodyne." This word comes from the Greek roots that suggest a substance or method that alleviates discomfort or pain. In medical and literary contexts, anodyne can describe both a specific pain-relieving medication and anything that serves to soothe or calm distress or anxiety.

The other options do not relate to the concept of pain relief. "Apogee" refers to the highest point in the development of something, especially in an orbit, lending itself more to the context of astronomy or a peak experience rather than pain relief. "Apostate" describes someone who has renounced a religious or political belief or principle, which bears no relevance to physical or emotional relief. "Artless" denotes a lack of artifice, sophistication, or guile, often used to describe someone who is natural or innocent, and again does not connect to the idea of alleviating pain. Thus, "anodyne" is the most appropriate word reflecting relief from discomfort.