deleterious weed growing in grain fields, c. 1300, from northern dialectal French darnelle; according to one theory the the second element is Old French neelle (Modern French nielle) "cockle," from Vulgar Latin *nigella "black-seeded," from fem. of Latin nigellus "blackish."
But perhaps rather the word is related to Middle Dutch verdaernt, verdarnt "stunned, dumbfounded, angry," Walloon darne, derne "stunned, dazed, drunk," the weed being so called from its well-known inebriating quality (actually caused by a fungus growing on the plant); the French word for it is ivraie, from Latin ebriacus "intoxicated," and the botanical name, Lolium temulentum, is from Latin temulent "drunken," though this sometimes is said to be "from the heavy seed heads lolling over under their own weight."
In some parts of continental Europe it appears the seeds of darnel have the reputation of causing intoxication in men, beasts, and birds, the effects being sometimes so violent as to produce convulsions. In Scotland the name of Sleepies, is applied to darnel, from the seeds causing narcotic effects. [Gouverneur Emerson, "The American Farmer's Encyclopedia," New York, 1860. It also mentions that "Haller speaks of them as communicating these properties to beer."]