In Greek mythology, Hypnos (/ˈhɪpnɒs/; Ancient Greek: Ὕπνος, 'sleep'),[2] also spelled Hypnus, is the personification of sleep. The Roman equivalent is Somnus.[3] His name is the origin of the word hypnosis.[4] Pausanias wrote that Hypnos was the dearest friend of the Muses.[5]