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 book of etymological hoaxes, How The Irish Invented Slang claimed that the English word shoo comes from the Irish sitheadh.
Sitheadh is pronounced shee-hoo or shee-ha it is defined by Ó Dónaill as ‘rush, dash, onrush, swoop’. The connection between these meanings and shooing someone or something is not very close and sitheadh is certainly not used when shooing chickens out of the door or telling children to go away. You might use fuisc or amachaigí in cases like this and the action would be described as an ruaig a chur ar dhuine.
The real derivation of shoo is well-known. It is an English word and it has always been an English word. It is found in English from at least the 15th century and it has a clear cognate in German scheuchen, which means to shoo.