Another utterly stupid claim made by Cassidy in his book, How The Irish Invented Slang, is that the English words mark or mark Anthony, slang terms for a sucker or target of a scam, derive from Irish. As usual, there is no evidence for this and plenty of strong evidence against it.
For one thing, while the word marc is Irish and means a mark, the word is a relatively modern borrowing from English and there is no evidence of it meaning target of a scam. In Irish, the earliest references date back to 1639, in the Catechismus of Tiobóid Galldubh (Theobald Stapleton).
In English, the word is very ancient. It had acquired the meaning of target by the year 1200. It was first used with the meaning of target of a scam or sucker in the 1880s.
As for Mark Anthony, a slang phrase which seems to appear first in the 1970s in America, Cassidy claims that this comes from marc andána, which he says means a rash mark. The word andána is an intensified form of dána, which means bold. Of course, there is no evidence of anyone actually saying or writing marc andána in Irish. The sole authority for its existence is one crazy man – Daniel Cassidy – who lived his whole life in the USA, never learned Irish and never acquired any qualifications.
And when you think about it, the whole thing is much more likely to be English than Irish. A mark is a target and has been since the middle ages. That word comes to be a term for the target of a scam. Then someone adds Anthony to it because everyone’s heard of Mark Anthony. It might also have been influenced by a work of 19th century Irish fiction, The Fortunes of Hector O’Halloran and His Man Mark Anthony O’Toole.
Isn’t that more likely as a scenario than Cassidy’s non-existent phrase marc andána?