For some time now, some of my on-line friends have advised me to provide a version of CassidySlangScam without the invective aimed at Cassidy and his supporters. In response to that advice, I am working on providing a glossary of the terms in Cassidy’s ludicrous book How The Irish Invented Slang with a short, simple and business-like explanation of why Cassidy’s version is wrong.
The origins of this slang term are fairly well-known. Lam meaning flight or escape comes from the word lam meaning to beat, which is found as early as the Middle English period. The modern slang term ‘on the lam’, which means on the run, is linked to expressions like to beat it for to escape.
Daniel Cassidy, in his work of false etymologies, How The Irish Invented Slang, claims that this comes from the Irish léim, which is pronounced roughly like English lame and means to jump.
There is no idiom in Irish “bheith ar an léim”, to be on the léim. The Irish for being on the run is ar a sheachaint (ar a sheachnadh) or ar a theitheadh, not ar an léim. Note also the casual dishonesty in Cassidy’s treatment of this word where he tries to pretend that the use of lam for beat in English can also be explained in terms of léim, as according to Cassidy, léim can mean to attack. In fact, just like English jump, you can say that someone or something leapt on a person to mean that they attacked them. That is very different from “lamming away at someone with both fists,” which has no Irish equivalent with léim.
In other words, this derivation is also nonsense, like nearly everything in Daniel Cassidy’s book.