The English word
hypnotic (and related words like hypnosis and hypnotize) come from the Greek language originally (the "y" is a good clue about that!), specifically from the Greek word
hypnos which means "sleep" (
ὕπνος). When something is hypnotic, that means it puts you into a state like that of sleep. In a medical context, like a "hypnotic drug," that means the drug is sleep-inducing.
Hypnos was also personified as the God of Sleep. His mother is "Night" and his father is "Darkness," and his brother is Thanatos, "Death." You can read more about the Greek god at
Wikipedia.
Here is a
bronze head of Hypnos, circa 100 C.E.: