Cassidy introduces his treatment of the word chuck as follows:
Chuck, v., chucking, vn., to throw, especially to throw or pitch a ball; tossing, discarding. Uncertain origin or onomatopoeic. (Chapman, 71; OED)
Cassidy’s claim is that “The Irish teilg (pron. chel’әg, throw) is spelled “chock” when it gets tossed into English slang in the 16th century.”
Why isn’t this true? Well, there are a couple of points to remember. One, Cassidy’s ‘system’ of referencing as shown above is completely inadequate. Cassidy gives information about the meaning and possible origins of the word. Then, he gives two different sources, Chapman and the OED. There is no way of knowing which pieces of information come from which books, or indeed if all the ‘information’ comes from either of them. It was a standard practice of Cassidy’s to slip in his own inventions in these multi-source definitions. And who is Chapman? Well, it’s hard to know when you’re dealing with a book with no bibliography, but I would assume it’s probably Robert Chapman of the Dictionary of American Slang. The OED states that chuck is probably from the Old French chuquer, later choquer, “to knock, to bump”. Other sources concur with this possible origin – for example, Eric Partridge’s Origins (originally published in 1958, though my edition was published in the 1990s). While it is not completely certain, it’s a reasonable guess. It was in Cassidy’s interests to pretend that there is no other possible origin because of the weakness of his own half-baked suggestion.
Another problem with Cassidy’s Irish origin is that the word chuck was first used at the end of the 16th century in English. Cassidy likes to claim that many words were borrowed this early from Irish but the only evidence for this is Cassidy’s own discredited words like dock from tobhach or queer from corr. In reality, there seems to have been little Irish influence on English as early as this (apart from words relating to warfare like kern and gallowglass and bonnaught, which the English had good reason to learn).
However, the main reason is that teilg doesn’t sound anything like chuck. Why would anyone borrow a word from Irish and pronounce it in a completely different way? And how can you prove a connection when the two words are so totally unalike?
Teilg does primarily mean to hurl or throw in modern Irish. It originally meant to release, to throw, to shoot a bow, to give birth, to shed tears. You can find a full list of meanings under telcud at the online dictionary eDIL (http://www.dil.ie/search?search_in=headword&q=telcud). It is pronounced something like chelleg in Ulster dialect while in the south it would be tellig. (You can find sound files for the three main dialects on focloir.ie: http://www.focloir.ie/ga/dictionary/ei/cast#cast__12)
In other words, not only is Cassidy’s claim unlikely, the choquer origin makes a lot more sense, which is why Cassidy pretended it didn’t exist. Which is another good reason to chuck your copy of How The Irish Invented Slang …