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.
Daniel Cassidy, in his work of false etymology, How The Irish invented Slang, claimed that the word ditch (as in ‘she ditched him’) comes from the supposed Irish phrase de áit? This is untrue. The phrase de áit isn’t in use in Irish and never has been.
The two words exist independently, of course. De means from or ‘off of’, ‘from the surface of’ (bhain siad an pictiúr den bhalla – they took the picture off of the wall), while áit means place. And occasionally they occur together in idiomatic phrases like an phrochlais sin de áit (that dump of a place) or taobh amuigh de áit (outside of a place) but in the standard language, this would usually become d’áit and it isn’t anything to do with displacing or dislodging or dumping in these cases. If you want to say that someone displaced something or put it out of its place you would use as áit, not de áit: cuireadh na brící as áit nuair a thit an scafall orthu (the bricks were dislodged when the scaffolding fell on them). So, de áit is pretty much impossible as the origin of ditch.
The English ditch, on the other hand, is a very likely source. A ditch, meaning a kind of trench at the side of the road (or sometimes the bank beside the trench in Ireland), comes from the Old English word dic. And in the old days, when you had some rubbish you dumped it in the ditch, or ditched it. In time, this became a general term for discarding or dumping.