soporific

"It is said that the effect of eating too much lettuce is 'soporific.' I have never felt sleepy after eating lettuces; but then I am not a rabbit." In The Tale of the Flopsy Bunnies by Beatrix Potter, the children of Benjamin Bunny were very nearly done in by Mr. McGregor because they ate soporific lettuces that put them into a deep sleep. Their near fate can help you recall the history of soporific. The term traces to the Latin noun sopor, which means "deep sleep." (That root is related to somnus, the Latin word for sleep and the name of the Roman god of sleep.) French speakers used sopor as the basis of soporifique, which was probably the model for the English soporific.