Hypnos (Ὑπνος), also known as Hypnus is the god of sleep, a son of Erebos and Nyx, and twin of Thanatos. His godly symbol is a branch of a poplar tree dipped into the River Lethe, the river of forgetfulness located in the Underworld.
Hypnus was depicted as a young man with wings on his shoulders or brow. His attributes included either a horn of sleep-inducing opium, a poppy-stem, a branch dripping water from the river Lethe (Forgetfulness), or an inverted torch.
He has a horn of sleep-inducing opium which he uses to lull both mortals and gods to sleep. In dreams, he opens two gates that the Oneiroi use to get through to the minds of people. The Gate of Horn provides prophetic dreams, while the dreams of the Gate of Ivory are misleading and deceptive. But the dreams each person gets depends on the individual.
Hypnus is the father of the Oneiroi gods of dreams who are led by Morpheus.
- His Roman equivalent was Somnus or Sopor.
The English word "hypnosis" is derived from his name, referring to the fact that when hypnotized, a person is put into a sleep-like state (hypnos "sleep" + -osis "condition). Additionally, the English word "insomnia" comes from the name of his Latin counterpart, Somnus. (in- "not" + somnus "sleep"), Hypnos as well as a few less-common words such as "somnolent", meaning sleepy or tending to cause sleep. Consequently, the condition for someone who cannot or has difficulty falling asleep is insomniac.