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.
Masher is a slang term for a young man of fashion who frequented 19th century theatres because of his devotion to the leading ladies.
There is a discussion of its origins here in an excellent blog post from Anatoly Liberman: http://blog.oup.com/2011/01/masher/.
And here’s another from World Wide Words: http://www.worldwidewords.org/qa/qa-mas1.html
Both of these sources are inclined to regard masher and mash as being extensions of the English word mash meaning to crush and both of them point to the similarity between the uses of mash and the uses of the word crush.
Cassidy’s claim was that it derives from the Irish maiseach, an obscure adjective meaning beautiful or elegant (according to Ó Dónaill’s dictionary, maisiúil is the usual adjective formed from maise. I wouldn’t use maisiúil or maiseach, though I use maise all the time in idioms like Ba d(h)eas an mhaise dó é, it was a nice thing for him to do). How an adjective meaning beautiful in Irish gave rise to a noun meaning lady’s man and a verb meaning to have a crush in English is not explained, but then very few of the claims made in Cassidy’s book stand up to any scrutiny at all.