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.
This is a slang term derived from jizz, which seems to have originally meant spirit or energy. It first occurs in 1842 with that meaning. Then it took the meaning of semen, apparently for similar reasons to the use of spunk for both courage and semen.
Its ultimate origins are unknown. What we do know for a fact is that it has no connection with Daniel Cassidy’s claim that jasm comes from the Irish ‘teas ioma’, which according to Cassidy, means ‘an abundance of heat, passion, excitement; fig. semen.’ Cassidy thinks the word iomaí (or ioma) is an ordinary adjective which can follow a noun. It isn’t and it can’t. Iomai is used in phrases like ‘Is iomaí oíche’ (it’s many’s the night). See: https://www.teanglann.ie/en/fgb/iomaí
In other words, this is not just a non-existent phrase in Irish, it could not exist. Even if it could, and teas ioma did mean excessive heat in Irish, why does Cassidy think that overheating and semen are the same thing in Irish, when they aren’t the same thing in any other European language?