It is true that Hypnos was the Greek god of sleep and that the word came into the English language after the Renaissance, once the classics were being read in England for the first time.
However hypnotic did not appear with reference to the Greeks, but in a medical discourse on urine in 1625 in which James Hart translates from Dutch and comments on the masterwork by the Dutchman Pieter van Foreest. The book states that hypnotic medicines should not be ignored. Here hypnotic means something inducing sleep. Fifty years later hypnotic appears in yet another translation of an important medical treatise. The work was written in Latin by Dr Willis, an English doctor who in the custom of the time wrote in the European language for science. A clear definition is given “hypnotic, a medicine that causes sleep” in the translation by Samuel Pordage – a poet and rival to Dryden.
In its current sense the word has a clear origin. Dr James Braid was known in two areas of research – the club foot and mesmerism. But he came to his own as the father of hypnotism. In 1841 he saw a demonstration on stage of what was then known as then animal magnetism. One year later, he published a Practical Essay on the Curative Agency of Neuro-Hypnotism defining it as “the state or condition of nervous sleep” and soon afterwards used hypnotism as a shortened version of the same. Ten years later, he published another book, Magic, Witchcraft, Animal Magnetism, Hypnotism and Electro Biology indicating that hypnotism had not yet made it in scientific terms.